Discover how LFP batteries became the top EV choice—safer, longer-lasting, and now just $115/kWh. Explore their evolution, innovations, and global impact.

The Rise of LFP Batteries: History, Cost & EV Dominance

LFP batteries have become the dominant battery in global EV production and have recently sharply fallen in price to a stunningly low $115/kwh.&nbsp;<h2>What Makes A Given Battery A Given Chemistry?</h2>Like other batteries, lithium-ion batteries have two electrodes, a cathode and an anode. The anode, which is the positive end in these batteries, is generally just graphite—nothing too special there. The cathode is where all the magic happens: that’s where the chemistry lives. It’s also the most expensive part of the battery, making up about 70% of the total value, and it’s the main distinguishing factor between different types of batteries.Two Main Categories: Ternary vs. LFPThere are two main categories of lithium-ion batteries: ternary batteries (made of three elements) and LFP batteries. Ternary batteries mix three different chemicals—either nickel, manganese, cobalt (NMC) or nickel, cobalt, aluminum (NCA)—in varying ratios. These batteries offer the highest energy density but use rare materials, making them more expensive. They’re also sourced from geopolitically tense regions and, due to their high energy density, have a greater risk of thermal runaway.LFP batteries use two different chemicals on the cathode—iron and phosphorus.&nbsp; There’s no nickel or cobalt, and iron and phosphorus are far more common worldwide. This makes LFP batteries much cheaper to produce and gives them a major advantage in cycle life: while NMC batteries retain about 80% of their capacity after 500–800 cycles, LFP batteries can exceed 2,000 cycles without significant degradation. If you’re looking to squeeze even more longevity out of your cells, check out our guide on <a href="https://cellsaviors.com/blog/get-more-cycles-from-lithium-ion-cells">How To Get More Cycles Out Of Lithium Ion Cells</a>.&nbsp;<h2>What Is The Downside Of An LFP Battery?</h2>&nbsp;The big drawback of LFP batteries is their lower energy density—around 90–150 Wh/kg compared to 260–300 Wh/kg for NMC and NCA. Two same-sized batteries, one LFP and one ternary, will store more energy if they use ternary chemistry. However, innovations in LFP chemistry, cell design, and pack integration have begun to narrow this gap. For a side-by-side comparison of these chemistries, see our full breakdown in <a href="https://cellsaviors.com/blog/lifepo4-nmc-chemistry-comparison">NMC&nbsp;Vs. LifePO4 Which Is Best</a>. It’s also important to remember that each chemistry (NMC, NCA, LTO, LFP) has many variations, and pack-level choices can significantly affect performance.&nbsp;<h2>Who Invented LFP Batteries?&nbsp;</h2>John B. Goodenough—yes, that’s his real name—first proposed and patented iron phosphate as a lithium-ion cathode material in the mid-1980s. His LFP chemistry promised better safety and cycle life but suffered from low electrical conductivity and poor energy density (around 90 Wh/kg), limiting its early appeal for electric vehicles.<h2>Why Are LFP Batteries So Cheap Now?</h2>The remarkable affordability of LFP batteries today is the result of many years of advances in materials science, strategic patent licensing and consolidation, and targeted policy incentives that drove early large‐scale adoption. By pooling and licensing key conductivity-enhancing patents, deploying subsidies to jump-start fleet electrification, and then allowing market forces to favor LFP’s inherent safety and longevity as subsidy support for higher-density chemistries waned, manufacturers achieved the economies of scale necessary to push prices sharply downward.Conductivity Boosts and Patent PoolsIn the 2000s, Canadian and European companies formed institutions to develop carbon-coating processes and related patents to enhance LFP conductivity. These patents were consolidated into a Swiss licensing consortium. In the 2010s, Chinese battery firms secured royalty-free domestic rights to these key LFP patents, whereas others worldwide had to pay licensing fees. Initially, Chinese firms could only use these patents domestically. China’s TVTC Policy and Early Adoption In 2009, China launched the TVTC policy (Thousands of Vehicles, Tens of Cities), a subsidy program encouraging local governments to deploy buses, taxis, and government vehicles equipped with LFP batteries. BYD then introduced LFP packs in its eBus and early hybrids, establishing domestic leadership. Outside China, most OEMs still preferred NMC or NCA for their higher energy density. Shifting Subsidies and Market Share Between 2016 and 2019, China shifted subsidies to favor EVs based on performance metrics (charge rate, range), prompting OEMs to chase higher-energy-density ternary chemistries. LFP’s share of new installations in China dropped from about 70% to 30% by mid-2019. Then, mid-2019, China halved its cash subsidies and continued annual cuts, narrowing the cost gap between ternary and LFP batteries. With subsidies rolling back, market forces favored LFP for its safety, cycle life, and lower cost—provided sufficient pack volume could compensate for lower energy density.<h2>Blade Cells and Cell-to-Pack Innovation</h2>In March 2020, BYD unveiled its Blade cells: ultra-thin prismatic LFP modules that eliminate intermediate modules in pack assembly. Traditional EV packs require cells → modules → packs; skipping the module step increases energy density at the pack level. BYD’s Blade-equipped Han EV achieves a 605 km range—about 85% of NMC density—while offering lower cost, better cycle life, and improved safety. Other Chinese OEMs swiftly adopted cell-to-pack (CTP) LFP technology, and by 2021 LFP pack volumes in China overtook NMC. By 2023, LFP accounted for 70% of EV installations in China.<figure data-trix-attachment="{&quot;contentType&quot;:&quot;image/png&quot;,&quot;filename&quot;:&quot;image.png&quot;,&quot;filesize&quot;:1466471,&quot;height&quot;:1080,&quot;href&quot;:&quot;https://admin.cellsaviors.com/storage/tau610n5FSkNiyI6qwh9zZQe6CaZLfE3opwqh4hT.png&quot;,&quot;url&quot;:&quot;https://admin.cellsaviors.com/storage/tau610n5FSkNiyI6qwh9zZQe6CaZLfE3opwqh4hT.png&quot;,&quot;width&quot;:1920}" data-trix-content-type="image/png" data-trix-attributes="{&quot;caption&quot;:&quot;BYD Blade Cells&quot;,&quot;presentation&quot;:&quot;gallery&quot;}" class="attachment attachment--preview attachment--png"><a href="https://admin.cellsaviors.com/storage/tau610n5FSkNiyI6qwh9zZQe6CaZLfE3opwqh4hT.png"><img src="https://admin.cellsaviors.com/storage/tau610n5FSkNiyI6qwh9zZQe6CaZLfE3opwqh4hT.png" width="1920" height="1080"><figcaption class="attachment__caption attachment__caption--edited">BYD Blade Cells</figcaption></a></figure><h2>Patent Expiry, Raw Materials, and Price Declines</h2>By 2022, core LFP patents began to expire, but China’s industrial base and supply-chain expertise were already dominant. New lithium sources in Australia, Chile, and Argentina came online, and by 2024 iron-ore prices fell ~15% due to a Chinese steel slowdown. LFP pack prices dropped another 20% to around US $115/kWh—making Chinese LFP packs the cheapest globally, even after import tariffs of 25–120%. In 2021, BYD began selling Blade batteries to Toyota, Ford, and others, sparking a price war among battery suppliers.<h2>Stationary Storage and Emerging Chemistries</h2>LFP’s cost and safety advantages have fueled a boom in grid-scale and home energy storage. Its lower energy density matters less for stationary applications. Innovations continue: adding manganese to create LMFP (a ternary lithium-iron-based cathode) boosts energy density, and novel two-step firing processes improve particle uniformity and conductivity.<h2>Conclusion</h2>LFP cell costs are destined to continue declining, and energy density gains may soon challenge NMC’s dominance. What began as an American-engineered, safe but low-energy chemistry has—through Chinese licensing, policy, and technological innovation—become one of the world’s lowest-cost and most promising lithium-ion battery technologies. We hope this article helped you learn more about LFP chemistry and lithium ion batteries in general. Thanks for reading!

A Brief History Of LFP Batteries

Explore modern battery types including alkaline, lithium, NiMH, lead-acid, and more. Compare primary vs. secondary batteries with real-world use cases.

Types of Batteries Today: Primary vs. Rechargeable

<h2>Battery Categories</h2>You can put any given battery in one of two categories. It’s either a primary battery or a secondary battery. A primary battery is a disposable or non‑rechargeable battery, while a secondary battery is a reusable or rechargeable battery. At first glance, you might think a primary battery is a rechargeable battery, but that’s just because we are from this era where rechargeable batteries have finally become good enough to be the most common kind of battery for many applications, so it just seems like they should be the 'primary' ones.<h2>Primary Batteries</h2>When it comes to primary batteries, we still use alkaline, zinc carbon, and lithium non‑rechargeable batteries. Pretty much all the other chemistries have gone by the historical wayside. Alkaline is the most popular type of primary battery, while zinc batteries are still used in developing parts of the world due to their extremely low cost.&nbsp;<h3>Alkaline</h3>Alkaline is still widely used in household devices like remote controls and flashlights. It’s extremely low‑cost. It has a very long shelf life. They can last up to 10 years, and they have a relatively stable voltage under load. They’re obviously non‑rechargeable, so you pay for them once and use them once rather than paying for them once and using them over and over again.<h3>Zinc Carbon</h3>In some parts of the world and in some niche applications, zinc carbon batteries are still used. It’s an older technology, and it’s generally only found in low‑drain devices. It’s extremely cheap to manufacture, which is pretty much the only reason it’s still used, but they have a very low capacity and their voltage drops pretty tremendously under even moderate loads, and they have a shorter shelf life.<h3>Lithium (Non‑Rechargeable)</h3>Another type of primary battery that’s become increasingly popular lately are lithium batteries. Usually we associate lithium batteries as being rechargeable, but in this case they aren’t. They are used in high‑drain or extreme‑temperature applications like in cameras, sensors, etc. They have extremely high energy density, a very long 10‑plus‑year shelf life, and a wide operating‑temperature range; but they are more expensive, and they have some safety considerations, as you’d expect with any other lithium‑ion battery technology, because they have such a low resistance that they can deliver a tremendous amount of current under short‑circuit situations.<h2>Secondary Batteries</h2>Now we’ve come to the secondary batteries, which are also known as rechargeable batteries.<h3>Lead Acid</h3>&nbsp;We still use lead-acid batteries in many applications. They’re still dominant in the automotive industry and they’re used as starter batteries. They’re still used as backup batteries in small-scale UPSs, which are uninterruptible power supplies, and some people still use them for off-grid solar, although you can make a pretty clear point that the total cost of ownership is actually higher with lead-acid batteries in that regard. Lead acid batteries have a very low cost per kilowatt-hour and they are extremely reliable. If you’re considering a retrofit, check out our guide on <a href="https://cellsaviors.com/blog/lead-acid-agm-lithium-replacement">How To Replace Lead Acid/AGM With Lithium </a>to see the potential benefits and pitfalls of moving to a lithium-based system. &nbsp;Lead-acid batteries are extremely heavy, very low-energy-density, and contain large amounts of lead that have to be contended with one way or the other.&nbsp;<h3>Nickel Cadmium</h3>Nickel‑cadmium batteries are still in use in some very old devices. There’s plenty of drills and things out there that were designed to run on nickel‑cadmium batteries, and they’re still working. They can tolerate extreme temperatures, and they have very high discharge rates. A major con of NiCd is the memory effect, and cadmium is very toxic; they’ve largely been phased out by nickel‑metal‑hydride.<h3>Nickel Metal Hydride</h3>Nickel‑metal‑hydride technology is still used in rechargeable AAs and AAAs and in some hybrid vehicles like the older Toyota Prius. NiMh batteries have a higher capacity compared to NiCd and less of a memory effect, but they still have a memory effect. They have a relatively high self‑discharge rate compared to other battery technologies and only a moderate energy density.<h2>Lithium‑Ion Rechargeable Batteries</h2>&nbsp;And now, of course, that brings us to the most popular type of battery of all time: the lithium-ion rechargeable battery. This thing is ubiquitous in consumer electronics such as smartphones, laptops, electric vehicles, and more. And you can even find it in industrial applications like grid-storage systems. There are many types of lithium-ion chemistries, but the three most popular are LCO, NMC, and LFP. If you’re looking to build your own pack from scratch, take a look at our step-by-step walkthrough in <a href="https://cellsaviors.com/blog/building-a-battery-pack-from-18650-cells">Building A Lithium Battery Pack From 18650 Cells</a>.&nbsp;There are many types of lithium‑ion chemistries, but the three most popular are:<ul><li>LCO (lithium cobalt oxide): Known for its extremely high energy density, and it’s used most of the time in phones and laptops. </li><li>NMC (lithium nickel manganese cobalt oxide): A close relative of LCO, it offers the best balance of energy, power, and longevity, and it’s mainly used in electric vehicles, phones, drills, RC applications, and more. </li><li>LFP (lithium iron phosphate): An up‑and‑coming chemistry with a much longer cycle life than the other two lithium‑ion chemistries; it’s much safer, and it finds the best use in stationary storage applications and some EVs that have the space and are efficient enough to not need a lot of capacity.</li><li><figure data-trix-attachment="{&quot;contentType&quot;:&quot;image/png&quot;,&quot;filename&quot;:&quot;image.png&quot;,&quot;filesize&quot;:1170178,&quot;height&quot;:1024,&quot;href&quot;:&quot;https://admin.cellsaviors.com/storage/cPljHUrCz9tdbskdqVBdlOlHk8Rz0TTgGiUmG9Ym.png&quot;,&quot;url&quot;:&quot;https://admin.cellsaviors.com/storage/cPljHUrCz9tdbskdqVBdlOlHk8Rz0TTgGiUmG9Ym.png&quot;,&quot;width&quot;:1024}" data-trix-content-type="image/png" data-trix-attributes="{&quot;presentation&quot;:&quot;gallery&quot;}" class="attachment attachment--preview attachment--png"><a href="https://admin.cellsaviors.com/storage/cPljHUrCz9tdbskdqVBdlOlHk8Rz0TTgGiUmG9Ym.png"><img src="https://admin.cellsaviors.com/storage/cPljHUrCz9tdbskdqVBdlOlHk8Rz0TTgGiUmG9Ym.png" width="1024" height="1024"><figcaption class="attachment__caption">image.png 1.12 MB</figcaption></a></figure></li></ul><h2>Why are batteries called AA, AAA, C, and D?</h2>At first, the battery names only went up in size. With A being the smallest battery, B being a little larger, and C even larger than that, and so on. But as technology progressed and devices and the batteries powering them actually ended up getting smaller, the only option was to use more As to signify than the new types were smaller than A. You can see a similar situation of wire gauges, its why we have 00, 000, etc.&nbsp;<h2>What Is The Most Common Type Of Battery Used Today?</h2>Lithium‑ion batteries are the most common type of battery used on earth today. This is because lithium ion batteries have such a high energy density, a high single cell voltage compared to other battery types, a low self‑discharge rate and no memory effect. They also have a long cycle life compared to other rechargeable batteries. Lithium ion batteries can be charged quickly, they’re extremely scalable and have form‑factor flexibility in their construction, and everybody’s making them right now. So the costs are coming down through economies of scale, and the battery‑management systems used to govern them have become extremely sophisticated, reliable, and low‑cost over time.Well, that pretty much covers it for what are the main types of batteries used today. We hope this article helped you learn more about the portable power landscape, thanks for reading!

What Are The Main Types Of Batteries Used Today?

Measure Internal Resistance With A Multimeter

Discover a straightforward method to calculate the internal resistance of lithium-ion batteries using a multimeter. Learn how to assess voltage drop, current, and battery efficiency in real-world conditions.

How To Measure Internal Resistance With A Multimeter

Measuring a lithium-ion cell’s internal resistance is super strait forward.: all you have to do is get three readings and do a bit of math. First, record the cell’s open-circuit voltage with no load attached. Next, apply a known load (or any practical load) and immediately note both the loaded voltage and the current flowing. Finally, subtract the loaded voltage from the open-circuit voltage to find the millivolts of drop, then divide that millivolt drop by the load current, and this will give you the cell’s internal resistance in milliohms.This single figure captures all the tiny ohmic losses hiding inside the metal, electrolyte, and connections of your cell. With that number, you can quantify efficiency under real-world loads.<h2>Understanding Inefficiencies and Ohmic Losses</h2>Nothing is 100 % efficient—there are always losses in any energy conversion or transfer. By identifying the processes that create those losses, we can calculate them rather than just wonder where they occur. In the case of extracting energy from a lithium-ion cell, most losses stem from ohmic resistance. Every conductor, even the most “ideal” ones, has some finite resistance determined by its material properties and geometry. To see how this plays out in a full health-check routine—including capacity tests and C-rate profiling—check out our <a href="https://cellsaviors.com/blog/steps-battery-testing">Battery Health Testing Process for Lithium-Ion Cells.</a>&nbsp;<figure data-trix-attachment="{&quot;contentType&quot;:&quot;image/png&quot;,&quot;filename&quot;:&quot;image.png&quot;,&quot;filesize&quot;:907784,&quot;height&quot;:1024,&quot;href&quot;:&quot;https://admin.cellsaviors.com/storage/VgI01XRjehc18wOnxGYpyGDZK3zmh0nsjZ6gs9hJ.png&quot;,&quot;url&quot;:&quot;https://admin.cellsaviors.com/storage/VgI01XRjehc18wOnxGYpyGDZK3zmh0nsjZ6gs9hJ.png&quot;,&quot;width&quot;:1024}" data-trix-content-type="image/png" data-trix-attributes="{&quot;presentation&quot;:&quot;gallery&quot;}" class="attachment attachment--preview attachment--png"><a href="https://admin.cellsaviors.com/storage/VgI01XRjehc18wOnxGYpyGDZK3zmh0nsjZ6gs9hJ.png"><img src="https://admin.cellsaviors.com/storage/VgI01XRjehc18wOnxGYpyGDZK3zmh0nsjZ6gs9hJ.png" width="1024" height="1024"><figcaption class="attachment__caption">image.png 886.51 KB</figcaption></a></figure><h2>What Determines Resistance?</h2><ul><li>Material: Copper and nickel paths of identical dimensions exhibit very different resistances—copper being far more conductive.</li><li>Geometry: A wide, flat plane of material has much lower resistance than a long, narrow strip of the same metal.</li><li>Cell Construction: In a battery, resistance arises from the casing, current collectors, electrode materials, electrolyte chemistry, and their interconnections—some in series, others in parallel.</li></ul>Ultimately, though, only the total internal resistance matters. We can measure it indirectly with any standard multimeter by comparing the cell’s voltage under no load to its voltage under load.<h2>Preparing to Measure Internal Resistance</h2>Regardless of the method you choose, you must:<ol><li>Measure the open-circuit voltage of the cell (no load attached).</li><li>Measure the loaded voltage immediately after connecting your load.</li></ol>The difference between these two readings, divided by the load current, yields the millivolt-per-amp drop, which directly corresponds to milliohms of internal resistance.<h2>Method 1: Known Resistive Load</h2>If you have a purely resistive load of known value, you don’t need to measure current directly—just apply Ohm’s law.<ol><li>Select your load resistor(s).<ul><li>Two 6 Ω resistors in parallel → 3 Ω total.</li></ul></li><li>Record the unloaded voltage.<ul><li>4.100 V.</li></ul></li><li>Connect the 3 Ω load and record the loaded voltage.<ul><li>4.010 V.</li></ul></li><li>Current &nbsp;I = Vloaded / Rload = 4.010 V / 3 Ω = 1.337 A</li><li>Voltage drop &nbsp;Delta V = Vopen – Vloaded = 4.100 V – 4.010 V = 0.090 V = 90 mV</li><li>Millivolts per amp and internal resistance &nbsp;Delta V per amp = 90 mV / 1.337 A ≈ 67.3 mV per A Internal resistance ≈ 67.3 mΩ</li></ol><h2>Method 2: Measured Current Load</h2>If you lack a known resistive load but can measure current, follow these steps:<ol><li>Connect your load (e.g., a motor or other device) to the cell.</li><li>Measure the open-circuit voltage. 4.100 V</li><li>Under load, simultaneously measure: Loaded voltage (4.010 V). Load current (with your multimeter in series (1.38 A).</li><li>Calculate Voltage drop &nbsp;Delta V = 4.100 V - 4.010 V = 90 mV</li><li>Determine Millivolts per amp and internal resistance &nbsp;90 mV / 1.38 A ≈ 65.2 mV per A Internal resistance ≈ 65.2 mΩ</li></ol><h2>Interpreting Your Results</h2><ul><li>Millivolts per amp = Milliohms. Once you have the mV/A figure, you’re done. </li><li>Efficiency guideline: Stay at or above 90 % efficiency under your expected load. In practical terms, ensure the voltage doesn’t sag by more than 10 % under typical current draw.</li></ul>Even with a basic $9 multimeter, you can achieve accuracy sufficient for most portable-electronics projects. More expensive meters simply yield tighter tolerances—but the principle remains the same. I cannot stress enough how important it is to be aware of voltage drop and its effects on not just a battery, but the entire circuit. If you know nothing about batteries, resistance, or anything like that, you can still compare the health and quality of various battery cells, simply by comparing how their voltages drop under the same kind of load.&nbsp; The battery cell that drops voltage the least with all else being equal is going to be the better battery cell.&nbsp;<h2>Do Multimeters Have High Internal Resistance?</h2>Yes. Multimeters have a very high internal resistance, generally on the order of 10 MΩ This wont make much of a difference when measuring voltages, but when measuring currents, it can cause quite a bit of error in cheap multimeters. The high resistance of a multimeter makes it safe to probe even very high voltages.&nbsp;<h2>Conclusion</h2>Measuring the internal resistance of a lithium-ion cell is a straightforward process: by comparing the cell’s open-circuit voltage to its loaded voltage under a known resistance or current, you can determine the voltage drop caused by internal losses. Dividing that millivolt drop by the corresponding load current directly yields the cell’s internal resistance in milliohms. Armed with this simple yet powerful method, you gain a clear, quantitative understanding of how much energy is dissipated inside your battery, helping you to optimize designs and troubleshoot performance in any portable-power application. If you’re ready to take individual cells and turn them into a robust pack, see our step-by-step guide on <a href="https://cellsaviors.com/blog/building-a-battery-pack-from-18650-cells">Building a Lithium Battery Pack from 18650 Cells.&nbsp;</a>We hope this article helped you learn more about how to measure internal resistance with a multimeter. Thanks for reading!

If you plan on designing a DIY solar setup for your home, shed, or RV, the heart of the system will be the battery bank

LiFePO4 battery banks in parallel

If you plan on designing a DIY solar setup for your home, shed, or RV, the heart of the system will be the battery bank. While there are several chemistries to choose from, LiFePO4 is often the best choice for home energy systems for several reasons. At some point you will be asking yourself, “How do you safely and efficiently connect multiple LiFePO4 battery banks in parallel?” &nbsp;(You can also check out our full guide on <a href="https://cellsaviors.com/blog/parallel-lithium-batteries">how to wire lithium batteries in parallel to increase amperage</a>.)&nbsp;Wiring LiFePO4 batteries in parallel is simple. All you have to do is connect all the positive terminals together and all of the negative terminals together. There is, however, some nuance involved depending on how much current your running, and how balanced your parallel connections are.In this article, we’ll go over all the ways you can wire LeFePO4 batteries in parallel, and we will explain how to maintain a proper balance of current when doing so.&nbsp;<h2>Why Choose LiFePO4 for Your Home Energy System?</h2>Lithium iron phosphate batteries have several different properties compared to the traditional NMC chemistry that most lithium-ion batteries use. And the most important one is the cycle life. Your typical NMC lithium-ion battery can be recharged 500–800 times before it's considered end of life, at which point it only holds 80% of the capacity that it used to, and its internal resistance will have by then increased dramatically.Lithium iron phosphate batteries, on the other hand, can last 2,000, 3,000, or even 4,000 cycles, depending on the quality of the cells and how you use them.&nbsp; Also, they have a more ideal voltage range for home energy applications, because most of the equipment that's used for home energy solutions — such as inverters, charge controllers, etc. — are made for either a 12 or 24-volt voltage range.Systems and their components exist outside of those values, but most of the time, home energy systems are either going to be in the 12 or 24-volt range.NMC In 24-Volt SystemsIt's relatively easy to make something 24-volt compatible using NMC cells because you can just put 7 in series. The full charge voltage would be 29.4 volts, the nominal voltage would be 3.7 times 7, which would be 25.9 volts, and the dead voltage would be about 2.8 times 7 for about 19.6 volts.So you've got around a 20 to 30-volt range with a 7S NMC lithium-ion battery. And because most 24-volt devices can work well within and even beyond that range, you won't have any problems.NMC In 12-Volt SystemsBut when you try to make 12 volts, you run into an issue. If you want to make 12 volts with NMC cells, you can try to put either 3 or 4 in series. Let's do both:<ul><li>3 times 3.7 is 11.1 volts, so that's close enough to 12 volts for the nominal voltage. But if you do the dead voltage around 2.8 times 3, you're down to 8.4 volts. Even if you raise your cutoff voltage to 3 volts, you're down to 9 volts. That's too low to operate a 12-volt system. </li><li>So let's try to add another cell in series. For 4S, we have a nominal voltage of 3.7 times 4. Well, that's 14.8. That's a little higher than 12 volts. It'd probably be okay. Most equipment that's made to run at 12 volts will cut off around 15 volts or something like that on the high end. So it would probably be okay.</li></ul>But remember, that's just the nominal voltage. That means you're losing all the capacity north of nominal voltage, because 4.2 times 4 is 16.8. That's way too high for any 12-volt system.LFP In 12-Volt SystemsBut we can compare that now to LFP. With LFP, you have a 3.7-volt maximum voltage and a 3.2-volt nominal voltage.&nbsp; So 3.7 times 4, and we get 14.8. That's the max charge voltage. That's about what an alternator puts out when it's charging your car, which is a 12-volt lead-acid battery. And then when those batteries are dead, around 2.8 volts, multiply that by 4, and we have 11.2. That's still well within the acceptable operating range of a 12-volt system.So, for any 12 volts system that's based on lead acid voltage ranges (and most are), the best type of battery to use is LFP. Doing that will ensure that you will be able to run your 12V equipment, regardless of the state of charge of your LFP cells in parallel.<h3>Why LFP Is Ideal For Home Energy Storage</h3>LFPs extremely high cycle life and its voltage range is what really makes them so ideal for home energy storage.&nbsp;The one big drawback of LFP is that they're much lower energy density than NMC. So they're going to be larger. They're going to have more volume. They're going to be heavier compared to an equal-capacity NMC battery. But the thing is, for home storage, that doesn't matter. That matters if you're doing an e-bike battery or something like that, that has to be small, compact, and lightweight. At that point, you would want to use NMC because it's got the best energy density.But for home energy storage, it doesn't have to be ultra-compact. And these batteries are still much more light, much more compact, and much more energy dense than the lead-acid batteries that they replace. And they last a whole lot longer. So for those reasons, LFP is definitely the best way to go for home energy storage.<h2>Wiring LiFePO4 Battery Banks In Parallel</h2>Can One 100Ah LFP Battery Power a House?You might think if you're just starting out that you could get a single 100 amp hour 12-volt LFP battery and run your entire house, but just not for very long. That's not the case because most of these batteries have around a 200 amp discharge current limit. At a nominal voltage of 12.8 volts, 200 amps is just 2.56 kilowatts.<figure data-trix-attachment="{&quot;contentType&quot;:&quot;image/png&quot;,&quot;filename&quot;:&quot;image.png&quot;,&quot;filesize&quot;:716809,&quot;height&quot;:970,&quot;href&quot;:&quot;https://admin.cellsaviors.com/storage/OfiPLxGnTdeciGv7aJedFujOFs1dE0dmqQG5qxou.png&quot;,&quot;url&quot;:&quot;https://admin.cellsaviors.com/storage/OfiPLxGnTdeciGv7aJedFujOFs1dE0dmqQG5qxou.png&quot;,&quot;width&quot;:2000}" data-trix-content-type="image/png" data-trix-attributes="{&quot;presentation&quot;:&quot;gallery&quot;}" class="attachment attachment--preview attachment--png"><a href="https://admin.cellsaviors.com/storage/OfiPLxGnTdeciGv7aJedFujOFs1dE0dmqQG5qxou.png"><img src="https://admin.cellsaviors.com/storage/OfiPLxGnTdeciGv7aJedFujOFs1dE0dmqQG5qxou.png" width="2000" height="970"><figcaption class="attachment__caption">image.png 700.01 KB</figcaption></a></figure>The average American household uses somewhere between 4 and 7 kilowatts of energy at any given point. It can go lower or higher than that, but that's a decent average to consider. So that means you have to put LFP batteries in parallel for increased current, even if you don't want the added capacity that comes along with that.<h2>Wiring LiFePO4 Battery Banks In Parallel: Two Methods</h2>There's two ways to wire batteries in parallel. You can do a simple daisy chain setup where one battery connects to the next battery in a row, and at one end of the row you'll have your positive and negative connections for energy to go in and out of the battery bank.Or you can do a star topology where all the batteries have the same length cables and connect to some central point.The Daisy Chain ArrangementThe first one we'll cover is the daisy chain arrangement. This can work fine in many applications as long as you consider:<ul><li>the amount of current that you're going to draw,</li><li>the amount of current that each battery can support, and</li><li>the amount of current that your parallel connections can take.</li></ul>For example, if you have three 100 amp hour LiFePO4 batteries wired in parallel and they can each do 200 amps of current, that means the battery bank as a whole can do 600 amps of current.Your series connections are extremely important when you're wiring LiFePO4 battery banks in parallel. If the cables can only do 200 amps each and you put a 600 amp load on the battery, in an ideal world each battery would see 200 amps of the load because it would be split three ways.But remember they're all connected with the same 200 amp cable, and the electrons will take the path of least resistance. So if you have one long cable that's the same width the whole way down, the further and further you go, the higher and higher the resistance.That means even if all of your LiFePO4 battery banks have the same resistance and they can all handle a very high current, if you have them in a daisy chain and you draw a high current from them, the battery closest to the terminals — the output — will see most of the load.It will be somewhat split amongst the batteries, but most of the load will be seen by that first battery. Its voltage will drop more than the batteries at the end because the batteries at the end are seeing a much lighter load.And then in an instant, right then and there, the batteries at the end will be charging the batteries closer to the terminals. This happens very quickly and ultimately isn't dangerous, but it does reduce the life of the batteries.Improving the Daisy Chain SetupThe best way to wire LiFePO4 battery banks in parallel, if you're going to do the daisy chain method, would be to use more and more cable to connect each battery further and further down the line.So you might use one positive and one negative cable for the first two batteries. And then for the next two batteries, you can use two positive and two negative cables. And then for the next two batteries, use four positive and four negative cables.That way, you don't have to use so many cables the whole way down, and doing this will help even out the resistance.If you don't want to do all that, then just make sure to keep your load at about half of your total current. So if you can support 600 amps, do 300 amps on the battery bank and it'll be just fine. But it will have a slightly reduced life because of that.The Star Topology ArrangementThe other way is by organizing them in a star topology. If you have all of your batteries surrounding an area where you want to put your terminals, you can simply use the same length cable to connect all of those batteries to that common terminal. This will make a circular-shaped setup, but it makes it extremely easy to get balancing just right.You could obviously arrange the batteries any way you want and just make sure you use the same length cable for each battery. But you'll end up with a bundle of cables somewhere or in multiple places if you do that — which is why I suggested the radial arrangement for connecting LiFePO4 battery banks in parallel while maintaining the balance of the parallel connections.<h2>Conclusion</h2>Whether you're expanding your DIY solar storage, setting up a battery backup generator, or preparing for the next power outage, understanding how to wire LiFePO4 battery banks in parallel is key.With the right wiring, proper charging using MPPT controllers,&nbsp; (learn more about the difference between <a href="https://cellsaviors.com/blog/mppt-pwm-solar-charge-controller">PWM and MPPT solar charge controllers</a>) , reliable equipment like Victron inverters, and smart safety practices, your battery bank will deliver dependable, long-lasting performance for your home, shed, RV, or off-grid retreat.

LiFePO4 Battery Banks in Parallel

This regulator board is really great with a power switch right there, but you can also control the output with the screen. 

Regulator board

<h2>Regulator Board Overview</h2>This regulator board is really great. It's a constant current buck converter, which means it lets you control the current and voltage settings. A buck converter, whether its constant current or not, can only reduce the voltage. It does not have the ability to increase the voltage. In this case of this buck converter, its almost not a problem at all. That's because this regulator board supports a relatively high 55V make input voltage.&nbsp;That means this regulator board can be attached to a 48V lithium ion battery, and be used as an excellent portable power supply that can also charge a wide array of other lithium ion batteries.&nbsp;<figure data-trix-attachment="{&quot;contentType&quot;:&quot;image/png&quot;,&quot;filename&quot;:&quot;image.png&quot;,&quot;filesize&quot;:933151,&quot;height&quot;:720,&quot;href&quot;:&quot;https://admin.cellsaviors.com/storage/j6xUep4o2wyXceRWl4i7w1yIkBpSQyDnanTY9vXb.png&quot;,&quot;url&quot;:&quot;https://admin.cellsaviors.com/storage/j6xUep4o2wyXceRWl4i7w1yIkBpSQyDnanTY9vXb.png&quot;,&quot;width&quot;:1280}" data-trix-content-type="image/png" data-trix-attributes="{&quot;presentation&quot;:&quot;gallery&quot;}" class="attachment attachment--preview attachment--png"><a href="https://admin.cellsaviors.com/storage/j6xUep4o2wyXceRWl4i7w1yIkBpSQyDnanTY9vXb.png"><img src="https://admin.cellsaviors.com/storage/j6xUep4o2wyXceRWl4i7w1yIkBpSQyDnanTY9vXb.png" width="1280" height="720"><figcaption class="attachment__caption">image.png 911.28 KB</figcaption></a></figure> Here, on the left side of the board, you can see the input. It's just those basic screw terminals, so you don't need any special equipment to use this board. <figure data-trix-attachment="{&quot;contentType&quot;:&quot;image/png&quot;,&quot;filename&quot;:&quot;image.png&quot;,&quot;filesize&quot;:1238537,&quot;height&quot;:720,&quot;href&quot;:&quot;https://admin.cellsaviors.com/storage/MRlFcJ0HjojldcrhGTC0uMDjxSXdmESUo7v4ePt6.png&quot;,&quot;url&quot;:&quot;https://admin.cellsaviors.com/storage/MRlFcJ0HjojldcrhGTC0uMDjxSXdmESUo7v4ePt6.png&quot;,&quot;width&quot;:1280}" data-trix-content-type="image/png" data-trix-attributes="{&quot;presentation&quot;:&quot;gallery&quot;}" class="attachment attachment--preview attachment--png"><a href="https://admin.cellsaviors.com/storage/MRlFcJ0HjojldcrhGTC0uMDjxSXdmESUo7v4ePt6.png"><img src="https://admin.cellsaviors.com/storage/MRlFcJ0HjojldcrhGTC0uMDjxSXdmESUo7v4ePt6.png" width="1280" height="720"><figcaption class="attachment__caption">image.png 1.18 MB</figcaption></a></figure> Here's the connections for the screen. Even though the connectors are the same for the screen, it's really easy to remember how to hook it up because the left side on the screen goes to the left side on the board, and the right side on the screen goes to the right side on the board.<figure data-trix-attachment="{&quot;contentType&quot;:&quot;image/png&quot;,&quot;filename&quot;:&quot;image.png&quot;,&quot;filesize&quot;:1144842,&quot;height&quot;:720,&quot;href&quot;:&quot;https://admin.cellsaviors.com/storage/GTRlZxIpOFjFJB7wA3nGO1EuUKerdYErvmUgJ0UB.png&quot;,&quot;url&quot;:&quot;https://admin.cellsaviors.com/storage/GTRlZxIpOFjFJB7wA3nGO1EuUKerdYErvmUgJ0UB.png&quot;,&quot;width&quot;:1280}" data-trix-content-type="image/png" data-trix-attributes="{&quot;presentation&quot;:&quot;gallery&quot;}" class="attachment attachment--preview attachment--png"><a href="https://admin.cellsaviors.com/storage/GTRlZxIpOFjFJB7wA3nGO1EuUKerdYErvmUgJ0UB.png"><img src="https://admin.cellsaviors.com/storage/GTRlZxIpOFjFJB7wA3nGO1EuUKerdYErvmUgJ0UB.png" width="1280" height="720"><figcaption class="attachment__caption">image.png 1.09 MB</figcaption></a></figure>There’s a power switch in the corner, but you can also control the output with the screen. <figure data-trix-attachment="{&quot;contentType&quot;:&quot;image/jpeg&quot;,&quot;filename&quot;:&quot;微信图片_20250428100434.jpg&quot;,&quot;filesize&quot;:125204,&quot;height&quot;:720,&quot;href&quot;:&quot;https://admin.cellsaviors.com/storage/rcxTbNkElCCkmLyLs7lCahYbpKQB5RyOPWg5xbxO.jpg&quot;,&quot;url&quot;:&quot;https://admin.cellsaviors.com/storage/rcxTbNkElCCkmLyLs7lCahYbpKQB5RyOPWg5xbxO.jpg&quot;,&quot;width&quot;:1280}" data-trix-content-type="image/jpeg" data-trix-attributes="{&quot;caption&quot;:&quot;Regulator board&quot;,&quot;presentation&quot;:&quot;gallery&quot;}" class="attachment attachment--preview attachment--jpg"><a href="https://admin.cellsaviors.com/storage/rcxTbNkElCCkmLyLs7lCahYbpKQB5RyOPWg5xbxO.jpg"><img src="https://admin.cellsaviors.com/storage/rcxTbNkElCCkmLyLs7lCahYbpKQB5RyOPWg5xbxO.jpg" width="1280" height="720"><figcaption class="attachment__caption attachment__caption--edited">Regulator board</figcaption></a></figure>Here is the output, on the right side of the board. It uses the same screw terminals as the input.&nbsp; A lot of regulator boards sold on Amazon and elsewhere claim a certain current rating, but in reality, come nowhere close. This regulator is different. It really can do what it claims to be able to do, and you don't have to modify it in any way for it to do so. So, that means you don't have to add a heatsink, a fan, or change out any connectors.&nbsp;<h2>Input Voltage and Capacitors</h2>On the Amazon page, it says a max input of 50 volts. It depends on the listing you're looking at and which part of the listing you're looking. But I can tell you it has 63-volt input capacitors and 63-volt output capacitors. I haven't checked the tolerances of the other chips, but I've run this reliably with a 55 volt input with no problems.As far as the output, the maximum of that output is going to be about a volt and a half lower than whatever the input is, but it still has its own maximum. I believe that's 51 volts.<h2>Fan and Thermal Protection</h2>It has a fan and that fan is really well done. What's special about the fan? Nothing. It's a cheap, low voltage, low current fan. It's the control system they're using that's nice. The fan only kicks on when it really needs to, and if that fan's running, this thing is not going to be hot – maybe just warm to the touch. You'd have to put it in extreme circumstances like maxing out the output current at 20 amps while having like a 40-volt difference between the input and the output for this thing to struggle. And if it does, it will cut off before anything gets damaged. I haven't had these burn up on their own. The only way I've broken these is by damaging the board, hooking it up backwards, or doing something else stupid. This thing works just as good as it says it will.<h2>Curious Connections and Screen Functionality</h2><figure data-trix-attachment="{&quot;contentType&quot;:&quot;image/png&quot;,&quot;filename&quot;:&quot;image.png&quot;,&quot;filesize&quot;:1723256,&quot;height&quot;:762,&quot;href&quot;:&quot;https://admin.cellsaviors.com/storage/KxdDW20YCjhZOl9QHB8eDVHIBz0l6h1xp2QziWzS.png&quot;,&quot;url&quot;:&quot;https://admin.cellsaviors.com/storage/KxdDW20YCjhZOl9QHB8eDVHIBz0l6h1xp2QziWzS.png&quot;,&quot;width&quot;:1447}" data-trix-content-type="image/png" data-trix-attributes="{&quot;presentation&quot;:&quot;gallery&quot;}" class="attachment attachment--preview attachment--png"><a href="https://admin.cellsaviors.com/storage/KxdDW20YCjhZOl9QHB8eDVHIBz0l6h1xp2QziWzS.png"><img src="https://admin.cellsaviors.com/storage/KxdDW20YCjhZOl9QHB8eDVHIBz0l6h1xp2QziWzS.png" width="1447" height="762"><figcaption class="attachment__caption">image.png 1.64 MB</figcaption></a></figure>It also has these curious connections in the corner of the board between the screen connectors. I’ve probed them while it’s running and while I'm changing settings. Some of these pins seem to be voltages that are proportional to whatever current and voltage that you set it to. I’ll have to look into that more later.Regardless of those pins and what they might do, there is opportunity here because I do believe the screen is I²C. If it's not I²C, it's some sort of basic digital protocol. So this cheap, low-quality screen could easily be replaced, and that's great because the cheap screen is the only complaint I have about this regulator.<h2>Applications and Performance</h2><h3>Powering Lower Voltage Devices</h3>What can you do with this regulator board? The most obvious thing to do with a <a href="https://cellsaviors.com/blog/buck-boost-converters">buck converter</a> is to power a lower voltage device with a higher voltage input.&nbsp;Suppose you’ve got a gadget rated for 12 V but only a 24 V battery in your toolbox. Dial the supply’s voltage down to 12 V and set a current limit above your device’s draw (say, 1 A), then feed the supply from whatever DC or AC source you choose. The internal regulator “drops” the excess voltage so your gadget sees a clean, stable 12 V and can’t pull more than the 1 A you allowed. Alternatively, if you have a separate DC‑DC converter, you’d configure it in exactly the same way: desired voltage and current limit, and it automatically adjusts its output around your load’s needs.So, consider something like a 12 volt LED strip. 12V strips can be ran at a little bit over 12 volts if you want some extra brightness at the expense of a lower operational lifespan. But you don't want to go too far; you definitely don't want to put 30 volts into it. It won't last very long and it'll get very hot. Its good to set the output voltage to somewhere around 14 and a half volts. If you go any higher than that and you're just not getting the brightness that you deserve for the power that you're putting into it.<h3>Alternative Uses: Multimeter Functionality</h3>You can actually stretch a simple adjustable DC bench supply into three surprisingly useful roles, all without firing up a true multimeter or charger. First, you can use it as a makeshift voltmeter: simply crank the supply’s output voltage to a value you know exceeds the unknown source, then dial the current limit down to zero.When you clip the leads onto your 7‑cell pack (nominally around 25 V), the supply immediately collapses its output to the battery’s actual open‑circuit voltage—say, 24.93 V—and since the current is set to zero, no current flows at all. It’s not a substitute for a real meter—you’ll lack reverse‑polarity protection and proper input impedance—but in a pinch it tells you the battery’s voltage without sourcing or sinking any current.<h3>Battery Charger</h3>Next, you can turn that same supply into a constant‑current, constant‑voltage battery charger. After measuring the pack at, say, 24.9 V, bump the supply’s voltage up to something safely above it—27 V works nicely—and set the current knob to your desired charge rate, for example 2 A. Plug in, and the supply automatically throttles its voltage down (to roughly 25.9 V in this case) so that exactly 2 A flows into the battery. If you then reduce the current limit to 1 A, you’ll watch the output voltage shift to around 25.6 V, because that’s the voltage required to push 1 A into the pack. Voilà: a DIY CC/CV charger.This regulator board makes a great custom battery charger, because you can set the voltage precisely. For example, if you have a 48V lithium ion battery, it has a full charge voltage of 54.6V. The problem is, that is 4.2V per cell, which is the absolutely maximum voltage that the cells can handle. You can charge your battery to 4V per cell, you will get a lot more life out of it in exchange for a small amount of capacity loss.&nbsp; With a normal charger, you can't do that. And chargers that are adjustable are often either expensive or poorly made. With this regulator board, however, all you have to do is set the output voltage to 52 volts. This will charge your 48V battery to 4V per cell, extending its overall lifespan.&nbsp;<h2>Battery-to-Battery Charging</h2>You can do exactly the same trick with a constant-current buck-converter regulator by using your higher-voltage pack as the “input rail” and letting the module’s CC/CV loop handle both current limiting and voltage regulation. To charge a 12 V battery from a 48 V source, first confirm the buck converter’s input stage can accept the full 48 V. Then adjust its output voltage pot to your battery’s recommended absorption or float voltage (for instance, about 14.4 V absorb and 13.6 V float on a lead–acid, or roughly 13.6 V for LiFePO₄) and set the current limit to the desired charge rate (e.g. 3 A for a 30 Ah lead–acid, or 0.1 C).Connect the 48 V pack to the converter’s VIN/GND terminals, clip its VOUT/GND leads onto the 12 V battery (mind the polarity), and the buck converter will step the higher voltage down to your setpoint, automatically throttling current until the battery’s voltage rises near the set value. At that point its CV loop takes over, holding the programmed voltage while the charge current tapers to zero and then maintaining a safe float.The same arrangement works for charging a single Li-ion cell (≈3.7 V nominal) from a 36 V pack. Hook up the 36 V battery to the input of the buck converter, and then simply set the output voltage to 4.20 V and the current limit to, say, 0.5 A (0.5 C for a 1 Ah cell). Then attach the cell to the output, and let the buck module automatically step down and regulate. It will supply a steady 0.5A while letting the voltage go to whatever it needs to be to maintain that current, up to the maximum set voltage of 4.2V. After that phase is complete, the regulator switches into CV mode keeps the voltage locked as current tapers off.&nbsp;<h2>Using the Regulator for Cell Group Charging</h2>You can also use a constant current buck converter to safely charge a cell group while its in series with other cells. All you have to do is connect the positive of the regulator output to the positive of the cell group, and the negative of the regulators output to the negative of the cell group that you are interested in. As long as the connections are touch just those places and no other places, you wont have any problems.&nbsp;All of these tricks rely on one simple fact: an adjustable bench supply is just a programmable voltage source with an adjustable current ceiling. Clamp the current at zero and it functions like a voltmeter; clamp the voltage and it acts like a charger; dial in a fixed voltage and it becomes a regulated power rail. The amperage you see is merely the load drawing whatever current Ohm’s law dictates at that voltage. Three tools in one little box<h2>Conclusion</h2>These 1000W buck converters are an incredible value. You get a robust, versatile power module that handles a wide range of input voltages and delivers adjustable outputs in both voltage and current. Whether you’re powering non-battery devices from a DC supply, AC mains, or even charging batteries, this little board does it all—and then some. You can <a href="https://www.amazon.com/EC-Buying-Adjustable-Converter-Regulator/dp/B0B38GYF74?tag=cellsavior08-20">grab yours on Amazon</a> for under 30 bucks.

The Best Constant Current Buck Converter

Why do lithium batteries sometimes burst into flames while charging? 

What Is Thermal Runaway?

Sometimes, when you charge <a href="https://cellsaviors.com/blog/lithium-cell-battery-safety">lithium ion batteries too fast</a>, they catch on fire. This could be the result of thermal runaway while charging. I say "could" because not all lithium ion battery fires are related to thermal runaway. If you have a fire related to thermal runaway, you're in for a really bad day.&nbsp;<h2>What Is Thermal Runaway?</h2>Thermal runaway, essentially, is when something gets so hot that it cannot stop getting other parts of itself hotter and hotter. Because things that experience thermal runaway are generally things that don't react well to heat, once you heat them up, they start to have reactions that produce more heat.Once the situation gets so bad, your internal thermal runaway will quickly transition to an external thermal runaway, in which now, instead of the unwanted heat propagating throughout a single thing, such as a battery cell, it will now be propagating through many battery cells as they all experience the cascading effects of thermal runaway.<h2>Thermal Runaway Explained</h2>We are gonna go on a bit of a tangent here, but bare with me. To effectively demonstrate thermal runaway, consider a piece of paper. It takes a certain amount of energy to cause that piece of paper to catch on fire. The paper is the fuel in the fire triangle, the air in the room is the oxygen, and the third part of the fire triangle is energy. As we know, in order to have fire, all three parts of the fire triangle must be present.If I rub that piece of paper with my hand, it's just not enough energy to make it catch on fire. I can probably get the paper warm so that if you feel it after I rubbed it really hard, you could feel the warmth, you can feel the energy that I put into the paper, but it just wasn't enough energy to cause the paper to catch on fire. However, there is a very common device that can be used to easily put more than enough energy in that piece of paper for it to catch on fire—it's called a lighter. If I take a lighter and I start a very, very small flame at the very, very corner of that piece of paper, that tiny little flame does not contain enough energy to burn up the entire piece of paper, but it does contain enough energy to burn up the tiny corner of the paper that it's on.One of two things will happen if I leave this unattended. It will either fizzle out and go to smoke, and the paper will stop burning, or it will experience thermal runaway. Thermal runaway would happen if the angle of the paper was just right so that the flame was touching more of the paper that was not burned yet, or if the wind or air currents in the room moved just right to spread the flame out in just the right way that the process became large enough to become self-sustaining. This is the basic principle of starting a fire.It's relatively easy to get something to smoke. It's even relatively easy to get a small flame, but it takes some level of skill or effort to actually build a proper fire and have it burn properly. When you build a successful fire that becomes self-sustaining, what you've done is you have successfully achieved thermal runaway.It's when the stuff is so hot that it just can't help but continue to get stuff next to it hot, and the amount of heat that's added to the additional material is enough for it to burn and therefore release more energy and heat up other things next to it. Once thermal runaway has been achieved, unless you suck all the oxygen out of the air, it will simply burn until there's no fuel left.<h2>How Does Thermal Runaway Happen When Charging Lithium Ion Batteries?</h2>Lithium ion batteries have specific charge and discharge limits. This is because batteries store their energy in the form of reversible chemical reactions. Those reactions are not instant, and they take some time to propagate through the entire cell. This time, and other factors, cause this process to have what is equivalent to placing a resistor in series.As you pass current through any resistor, the voltage is going to drop. That voltage drop multiplied by the current will give you the amount of power, in watts, that is dissipated within the cell.&nbsp;<figure data-trix-attachment="{&quot;contentType&quot;:&quot;image&quot;,&quot;height&quot;:372,&quot;url&quot;:&quot;https://lh7-rt.googleusercontent.com/docsz/AD_4nXePbUKA9-G5tB1V4mL7Qe99EbTt2OALlY41TWJRMcVOkdcfkV03FzRvu2E1qsBYZDPp4UW6wkGJHkjGKqlfRw3sFe0MFg4LRmF_kqjxfzpfkiLkxtlPLwfnXlJI4_A4wUndsnfOTw?key=Tfa1Yg0FDhtXjhNSTLpoNM0u&quot;,&quot;width&quot;:624}" data-trix-content-type="image" class="attachment attachment--preview"><img src="https://lh7-rt.googleusercontent.com/docsz/AD_4nXePbUKA9-G5tB1V4mL7Qe99EbTt2OALlY41TWJRMcVOkdcfkV03FzRvu2E1qsBYZDPp4UW6wkGJHkjGKqlfRw3sFe0MFg4LRmF_kqjxfzpfkiLkxtlPLwfnXlJI4_A4wUndsnfOTw?key=Tfa1Yg0FDhtXjhNSTLpoNM0u" width="624" height="372"><figcaption class="attachment__caption"></figcaption></figure> Why Do Lithium Ion Cells Get Warm While Charging?It's a little known fact that the lithium ion charging process is actually endothermic, so that means it absorbs heat, but this effect is only at a few milliwatts. The reason cells don’t feel cool to the touch and still get warm while charging is because of the heat generated by ohmic resistance, which is actually a bit higher in the charging direction.&nbsp;Also, as a lithium ion battery reaches its full charge voltage, its resistance creeps up a little further, adding more heat to the system. &nbsp;So we know that battery cells get warm when any current is passed through them, and we know they get warmer as they're charging, despite the charging process itself actually absorbing a little heat.And we know what thermal runaway itself is, so we can put it all together into one package and clearly see that if you charge a battery pack too quickly, it can experience thermal runaway and cause a very bad chain reaction.As a battery gets older and older, its resistance increases, but the charger you’re using doesn’t know the age or health of the battery, so it’s going to charge it with the same current it always does.So what that means is, for any lithium-ion battery, every time you charge it, it gets a little hotter during the charging process because its resistance increases over time. This just happens very slowly.If the <a href="https://cellsaviors.com/blog/bms-lithium-batteries">BMS doesn’t have a temperature sensor</a>, and if the battery was already built in a way that it was going to get hot under charge normally—because it doesn’t have enough cells for the amount of current being put into the battery—towards the end of that life span, that battery just may tip over into the danger point as it becomes hotter and hotter under charging, and it could experience thermal runaway.A lot of the time, the BMS will be able to support a certain amount of charge current that’s above the amount the cells can support, but the manufacturer supplies the charger, and it’s a small charger—like a 2 or 3 amp charger—so they don’t think anything of it.But the customer wants a faster charger, buys an appropriate-voltage lithium-ion charger and an adapter, or finds one with the right connector, and everything works fine.The BMS has a 10 amp limit; the cells can only handle 5 amps of charge current, and he’s got a 6 amp charger.In this situation, everything will work fine most of the time, but after a really hard ride, where the cells are already hot from discharge, and you throw it on a charger that overloads it, you could have a serious problem on your hands.<h2>Final Thoughts</h2>In the end, thermal runaway while charging a lithium-ion pack really comes down to a vicious feedback loop: you shove current in faster than the cells can comfortably absorb, they heat up from resistive losses (and even absorb a little heat as they charge), and as their internal resistance creeps up with age or state of charge, they heat up even more.If that extra heat can’t be whisked away––either because the cell layout doesn't have enough cells in parallel, the BMS has no temperature cut-off, or you’ve simply over-amped the charger ––you’ve lit the fuse for a cascading fire. Once one cell tips over into thermal runaway, it will ignite its neighbors until the whole pack goes up in smoke (or worse). So, bottom line: respect the cell’s charge limits, match your charger and BMS to the battery’s capabilities, and keep an eye on temperature. Push it too hard, and you could easily have a heat related catastrophe.&nbsp;

Thermal Runaway While Charging

The age old debate of voltage vs current in article form.

Voltage Or Current - Which Kills You

So, is it the voltage that kills you or is it the current? The age-old question—endlessly debated for well over a century.Voltage can be thought of as the pressure of the electricity because voltage is literally the energy per unit charge of the electricity. Resistance is the amount in which a given material will resist the flow of that electricity, and current is the rate at which that electricity ends up flowing considering the amount of energy it had in the first place and how difficult it is for that energy to move through a given material. In this article, we will explain in depth what voltage, current, and resistance are. We will also explain how those things combine to form power. This might be somewhat of a controversial article, but let's get started.<h2>What is Voltage?</h2>Voltage is, quite literally, the measure of the potential energy per charge between two points. Put simply, voltage is the ability for a given material to create electricity. In order for electricity to happen, you have to have two things that have a difference in charge come into contact. Once that happens, that creates a voltage at that moment—that is when voltage is created.A <a href="https://cellsaviors.com/blog/diy-bench-power-supply">power supply </a>creates a voltage like this. It uses various devices, components, and techniques to increase the charge on one side of the circuit while keeping the charge on the other side at a particular reference point. This difference in charge creates the voltage. Voltage only exists when there is a difference; if there is no difference in charge, there is no voltage.Humans are really smart, so we can make all kinds of devices and combine all kinds of materials to control the charge of a particular thing. We can do that so well that we can control the charge between two particular things so precisely that we can produce exactly 12 volts of difference. Whenever you refer to voltage, you're really referring to how many volts of difference there are—because voltage is, by definition, a difference. If there's no difference, there is no voltage.A battery creates a voltage like this. We create two different materials that, by their very nature, have two different levels of charge. We keep those materials separated so that they don't come into contact inside the battery. Then, we connect conductors to the outside of the battery so we have a positive and negative terminal.&nbsp;<figure data-trix-attachment="{&quot;contentType&quot;:&quot;image/png&quot;,&quot;filename&quot;:&quot;微信图片_20250418093406.png&quot;,&quot;filesize&quot;:1307805,&quot;height&quot;:1024,&quot;href&quot;:&quot;https://admin.cellsaviors.com/storage/f5D9D4s6eYeZ7VySHrsA4oQjozWYiJxQKrai3pcW.png&quot;,&quot;url&quot;:&quot;https://admin.cellsaviors.com/storage/f5D9D4s6eYeZ7VySHrsA4oQjozWYiJxQKrai3pcW.png&quot;,&quot;width&quot;:1024}" data-trix-content-type="image/png" data-trix-attributes="{&quot;caption&quot;:&quot;Battery voltage diagram&quot;,&quot;presentation&quot;:&quot;gallery&quot;}" class="attachment attachment--preview attachment--png"><a href="https://admin.cellsaviors.com/storage/f5D9D4s6eYeZ7VySHrsA4oQjozWYiJxQKrai3pcW.png"><img src="https://admin.cellsaviors.com/storage/f5D9D4s6eYeZ7VySHrsA4oQjozWYiJxQKrai3pcW.png" width="1024" height="1024"><figcaption class="attachment__caption attachment__caption--edited">Battery voltage diagram</figcaption></a></figure><h2>What is Resistance?</h2>This one's pretty easy to conceptualize, because resistance literally is just that—it is the resistance to the voltage, or how much it's going to lower the voltage. Resistance is the property of the material that defines how much the input voltage will be different from the output voltage. And one might interject and say, well, actually, a resistor regulates the flow of current in a circuit. Right, but how does it do that? If you are interested in resistance, then check out our article on resistance and <a href="https://cellsaviors.com/blog/the-effects-of-reistance-on-a-battery">how it affects a battery's performance</a><h2>How Does A Resistor Limit Current?&nbsp;</h2>A resistor affects the current flow by creating a voltage drop across itself, so it is lowering the voltage along the path of the circuit. Here is how it happens:&nbsp;<ol><li>In a circuit, with a voltage source (like a battery), the total voltage from the source remains constant (say 12V).</li><li>When current flows through a resistor, it creates a voltage drop across that resistor according to Ohm's Law (V = IR).</li><li>This voltage drop means that the electric potential decreases as current moves through the resistor - so yes, the resistor is effectively "lowering the voltage" at points after it in the circuit.</li><li>The resistor limits current flow because the voltage drop it creates must obey Ohm's Law. Since the voltage source is fixed, the current must adjust according to I = V/R.</li></ol>For example, in a simple circuit with a 12V battery and a 4Ω resistor, the current will be 3A because I = V/R = 12V/4Ω = 3A. The resistor creates a 12V drop across itself, and this voltage drop is what limits the current to 3A.<figure data-trix-attachment="{&quot;contentType&quot;:&quot;image/png&quot;,&quot;filename&quot;:&quot;微信图片_20250415152634.png&quot;,&quot;filesize&quot;:1558076,&quot;height&quot;:1024,&quot;href&quot;:&quot;https://admin.cellsaviors.com/storage/wVnEKpEx7uDYjMDQ3d2rfP3yRk6XeLzbbNnriyqP.png&quot;,&quot;url&quot;:&quot;https://admin.cellsaviors.com/storage/wVnEKpEx7uDYjMDQ3d2rfP3yRk6XeLzbbNnriyqP.png&quot;,&quot;width&quot;:1024}" data-trix-content-type="image/png" data-trix-attributes="{&quot;caption&quot;:&quot;Basic Circuit with Resistor&quot;,&quot;presentation&quot;:&quot;gallery&quot;}" class="attachment attachment--preview attachment--png"><a href="https://admin.cellsaviors.com/storage/wVnEKpEx7uDYjMDQ3d2rfP3yRk6XeLzbbNnriyqP.png"><img src="https://admin.cellsaviors.com/storage/wVnEKpEx7uDYjMDQ3d2rfP3yRk6XeLzbbNnriyqP.png" width="1024" height="1024"><figcaption class="attachment__caption attachment__caption--edited">Basic Circuit with Resistor</figcaption></a></figure>So, resistors do work by creating a voltage drop, which directly limits the current flow. In practical terms, we can absolutely think of resistors as lowering the voltage along the path of current flow.The difference between the input voltage and the output voltage of a resistor is directly related to the rate at which the voltage is moving through the resistor. So if the voltage is moving through the resistor twice as fast, then it will produce twice as much voltage drop.Imagine a fluid that an object is entering at a given speed, and it's attempting to pass through this fluid. The speed when exiting this fluid will be lower than the speed at the time of entering the fluid. If resistance is the fluid, then we can think of resistance as a type of material that, the faster you try to move through it, the more your exit speed will be reduced. Traditionally, we might think of a bullet going through a block of ballistics gel—in that situation, the more speed you have going in, the more speed you're going to have going out, even though the speed will always be lower. But in this situation, resistance has the properties such that as you move through it faster, its ability to slow you down increases instead of decreases.<h2>Electronics Work At The Quantum Level</h2>I know that sounds really strange, but that's okay because we are literally dealing with the quantum world here. The things that we are describing with volts, current, amps, ohms, resistance—all of that is just our way to classically describe a quantum thing. Quantum things don't have to obey classical physics.For example, if we have a certain amount of balls in a given amount of space, we can absolutely predict with a very high degree of accuracy exactly where those balls are because we can measure them. But electrons can't be measured like that. We can only predict with a certain degree of accuracy the probability of their position at any given point. We can't even say with certainty that an electron is not two feet from its nucleus. All we can say with certainty is that it's 0.0001% likely to be there, so basically unlikely to be there.And as you get closer and closer to where they actually are, the probability that they are there increases to almost, but never, 100%. This doesn't make classical sense, but it makes quantum sense. So we don't really have to understand why these things are happening; we just have to understand that it's true that they are happening, and we have to be able to relate how it will happen and what those effects will be with mathematical certainty. We don't have to be right about it, it just has to work.<h2>What is Current?</h2>Current is the rate that the electricity moves through the circuit. It is the rate in which electric charge flows. So, consider a two-ohm load with a 12-volt circuit. A circuit by definition connects back around to itself—that's why it's called a circuit. If we increase the charge on one side of the circuit to whatever level is required to produce 12 volts of difference when connected to the other side of the circuit, and put a two-ohm load in series with that, electric charge will flow. And the rate in which it flows, we measure in amps.Ultimately, power supplies generate power that can be used because they maintain the difference between the high side and the low side of their outputs, and they are rated to maintain that difference up to a certain amount of speed. So, we can follow the entire path to see exactly when current is created. You either have a power supply that has active components or a battery that has material properties that produce two components that have different charges. When those two components come into contact, a voltage is created up to a particular maximum voltage. The actual voltage that's created depends on not just the resistance of the contact, but the resistance of the inside of the power supply or battery and every other part of the circuit—the wires, the connectors, the solder joints, the welds, the crimps; it all adds up.That means we can't just consider the resistance of the load, which is two ohms. We also have to consider the sum total resistance of everything else. So, let's just say, for simplicity's sake, that the entire power supply and circuit and everything is 140 milliohms. We add that to our two-ohm figure. Current is the measure of the end result speed of the electricity moving through a given material. It's easy to find the speed because all you have to do is divide the voltage by the resistance.If we take 12 volts and divide that by 2.14, we get 5.61. We know the speed of the electricity moving at any point throughout the circuit is 5.61 amps. The amount of power that happens as a result of that can be calculated by multiplying that speed by the voltage drop over a given section of the circuit. That comes out to 62.94 watts—that's the power for the entire circuit. But because only around 0.79 volts of that total voltage drop happens outside of the load, only a very small portion of the power is dissipated there. The overwhelming majority of the power goes to where there is an 11.22-volt drop across that two-ohm resistor, the load.So, current itself, while it's very important, is just the end result of how electricity moves through resistance. With a given voltage and a given resistance, the energy will be able to move through that circuit at a given speed. If it's 12 volts and 6 ohms, the speed will be 2 amps. If it's 5 volts and 2.5 ohms, the speed will also be 2 amps. If it's 100 volts and 1,000 ohms, the speed will be 0.1 amps. Multiply the speed by the voltage, and you get the power. That's how the current is the same through the wires, connectors, and everything else, but most of the power isn't going there because the voltage drop in that area is lower, because the resistance is lower.<h2>What Kills You? The Volts or the Amps?</h2>So, what kills you? The volts or the amps? The answer is either or, or maybe both. I mean, you could also say it's the resistance that kills you; you could also say it's the charge that kills you. We could trace it all the way back through the conservation of energy, matter, momentum, and all of that stuff, and we can say the big bang is what really killed you. But the order of operations is important. The voltage definitely happens first, and the amps are just the speed that that voltage is happening.So, what kills you? The bullet or the speed at which the bullet made contact with you? Technically, both of those things are true. If a much lighter thing hit you at the same speed, you wouldn't die. And if a much heavier thing hit you at a slower speed, you would die.So, when it comes to what kills you—the volts or the current—the current is the one actually doing the killing. But if you don't have enough voltage, there will not be enough current to harm you because of the resistance of the human body. Another thing to consider is the fact that, ultimately, the voltage is the star of the show. It's the voltage that may or may not be limited enough by the resistance to kill you or not, and the current is just the end result—the speed of the electricity moving through that resistance. And you have to multiply that by the voltage anyway to get enough watts to kill you. So, I feel like it's the voltage that kills you.

Is It The Voltage That Kills You Or The Current

A full breakdown of the benefits of a 72V battery

The Benefits Of A 72V Battery

Ah yes, the 72 volt battery, the ultimate goal for any e-bike enthusiast. And while the 72 volt battery is desired by so many, they can often be misunderstood. In this article, we'll talk about all of the benefits related to 72 volt batteries, whether a 72 volt battery is worth it, and what really are the performance and efficiency benefits when considering a 72 volt battery over, say, a 48 volt battery or a 52 volt battery. We'll answer some other key questions, such as: can you combine two 36 volt batteries to make one 72 volt battery? And much, much more. So, let's get started.<h2>What Is A 72V Battery?</h2>First of all, what is a 72 volt battery? Well, that quickly brings us to a problem. Batteries are given a voltage just to make it easy to explain them to people. In reality, a battery is never 72 volts. A 12 volt battery is never 12 volts. It's not 12 volts most of the time; it's not 12 volts a good chunk of the time—it’s basically never 12 volts. How batteries work is they have some sort of voltage, and as you use them, the voltage falls. So, a 72 volt battery, if it had a full charge voltage of 72 volts, would never be a 72 volt battery because the voltage would immediately start falling.<figure data-trix-attachment="{&quot;contentType&quot;:&quot;image/png&quot;,&quot;filename&quot;:&quot;yp8OSsd4raWXJYqzh7Xd6EW26GGQjaTT1ZIhwuzo.png&quot;,&quot;filesize&quot;:1373358,&quot;height&quot;:644,&quot;href&quot;:&quot;https://admin.cellsaviors.com/storage/OkQMPqjINo6hKvbFpF8StqccAWkasjY1oGBQ8Tlg.png&quot;,&quot;url&quot;:&quot;https://admin.cellsaviors.com/storage/OkQMPqjINo6hKvbFpF8StqccAWkasjY1oGBQ8Tlg.png&quot;,&quot;width&quot;:855}" data-trix-content-type="image/png" data-trix-attributes="{&quot;caption&quot;:&quot;image.png 1.31 MB&quot;,&quot;presentation&quot;:&quot;gallery&quot;}" class="attachment attachment--preview attachment--png"><a href="https://admin.cellsaviors.com/storage/OkQMPqjINo6hKvbFpF8StqccAWkasjY1oGBQ8Tlg.png"><img src="https://admin.cellsaviors.com/storage/OkQMPqjINo6hKvbFpF8StqccAWkasjY1oGBQ8Tlg.png" width="855" height="644"><figcaption class="attachment__caption attachment__caption--edited">image.png 1.31 MB</figcaption></a></figure><h2>Battery Voltage And Chemistry</h2>'We get to these battery voltage numbers by using something called the cell's nominal voltage. For NMC chemistry—which is the most popular type of lithium ion battery—the nominal voltage is 3.7 volts per cell. So, to get to 72 volts, you have to put 20 of those cell groups in series. The funny thing is that doesn't even bring you to 72 volts; that brings you to 74 volts. Then, we have to go back to the data sheet and realize that sometimes they go by 3.6 volts nominal voltage, other times they go by 3.7 volts. It doesn't really have much to do with the chemistry specifically—it's more about marketing. Because regardless of a 3.6 volt nominal or a 3.7 volt nominal cell, they never go to those voltages. That's just an average of the general area it's going to be most of the time. It's true that the cell voltage starts to fall quickly when it's at 4.2, then slows down as it gets closer to 3.7, and then speeds up again as it's leaving that area. But it never goes to 3.7 or 3.6. If it ever is 3.7, it's for a fleeting, tiny moment. The point I'm trying to make is that there's really no such thing as a 72 volt battery; but we've got ourselves in this situation where we call a certain type of battery a 72 volt battery. That's generally going to be a battery that has a nominal voltage of 72 volts. You get to that by putting a certain amount of cell groups in series. If it's NMC chemistry, as I just said, it takes 20 cell groups in series. But LFP, which is another popular lithium ion chemistry, has a lower voltage. So, you take the 72 volts and divide that by 3.2, and you get 22.5. And since we can't do half a cell group, we have to do 23 cell groups in series. That means if you have a 72 volt battery that's made with NMC chemistry, it will have a voltage range of about 60 volts to 84 volts. But if you've got a 72 volt battery with LFP chemistry, it's got a voltage range of about 62 to 85.1 volts. It's pretty confusing, right? The good news is that generally any 72 volt device will work in the range of a 72 volt battery, and there's always some amount of wiggle room there. So, to get back to the question of what is a 72 volt battery, with today's common battery technologies, that would be a lithium ion NMC battery that has 20 cell groups in series, a lithium ion LFP battery that has 23 cell groups in series, or a lead acid battery with a whopping 36 cell groups in series because of the stunningly low nominal voltage of 2.0 volts.<h2>Combining Two 36 Volt Batteries to Make a 72 Volt Battery</h2>So, can you combine two 36 volt batteries to make a 72 volt battery? Yes, you can, but you can only use it until one of them dies. I'll explain.If you're combining batteries—and using batteries and all of that—I'm just going to go ahead and assume that you're using a BMS. If you're not using a BMS, then we have a whole additional problem, and you should probably check out our <a href="https://cellsaviors.com/blog/bms-lithium-batteries">article on BMS</a>.<h2>Understanding the BMS (Battery Management System)</h2>Combining two 36 volt batteries into one 72 volt battery requires that both of those batteries have a BMS. You'll run into this issue:First of all, I’ve got to do a quick primer on a BMS. A BMS keeps track of all the important stuff going on in your batteries, like the individual cell voltages, the current, and stuff like that. If anything goes out of spec, it turns the battery off. It's able to do that because all of the current flows through a MOSFET, and it can control the gate of that MOSFET and use it as a switch to control the flow of current.The MOSFETs used as switches inside a BMS are rated for a particular voltage. They can't handle just any voltage. The company that manufactures the BMS is going to select the most economically viable MOSFETs for the job. So, you can bet that the MOSFETs inside a 36 volt BMS aren't going to be rated for much more than the max charge voltage of a 36 volt battery.&nbsp;Seeing as we know the max charge voltage of a 36 volt battery is 42 volts, and we know the MOSFETs on the inside of the BMS will be able to handle at least that—and probably a little bit of buffer unless they're a really, really shady electronics manufacturer—this means you can probably get away with maybe 50 or 52 volts, but it's hard to find MOSFETs rated for that voltage. So, then you pick the next one up, which is usually 60 volts.If you notice something about 60 volts, it's less than 72 volts. And 72 volts isn't always the voltage of a 72 volt battery; remember, it could be as high as 84 volts. Some people might interject and say, "Well, I've hooked two 36 volt batteries with BMS up together, and they work just fine." Yes, that's true. Even though those transistors are not rated for the combined voltage, they don't see the combined voltage—because that's how transistors work. They have an extremely high resistance (basically an insulator when they're off), but they have an extremely low resistance (basically a conductor when they're on).That means when they're on—when both batteries are charged and working—the path from gate to source is going to have almost no voltage drop. The only voltage drop you're going to see is the drop over the transistor itself, which is very power efficient. So, that voltage drop is going to be very low, and it's going to work just fine. But the moment one of those batteries dies, it will send the signal to the gate of its MOSFETs and it will turn off the MOSFETs, at which point the resistance will be very high.Then, those MOSFETs will see the voltage of both batteries combined. You may even get lucky in this situation and not burn up your BMS. A lot of the time, it'll fry the BMS immediately. Other times, smoke will start pouring out of the batteries. There's a lot that can happen. Most of the time, you just wonder why you can't charge your battery again—it’s because one of them died and it fried itself from that effect.So, the answer to the question of "can you put two 36 volt batteries together in series to make a 72 volt battery?" is: yes, as long as neither one of them dies while you're using it. So, if you don't have far to go, or if you just want to do a drag race or some experiment, then okay. If you have two large 36 volt batteries—or even two batteries that have wildly different capacities—as long as the smallest of the two has more than enough energy for you to do what you need to do, then yes, you can put two 36 volt batteries in series to make a 72 volt battery.<h2>Benefits of a 72 Volt Battery: Performance and Efficiency</h2>So, what are the benefits of a 72 volt battery? What does the higher voltage give you in terms of power? And what efficiency improvements come along with that?Well, in terms of power, it works like this: If you have a motor that operates at 36 volts and it consumes 10 amps, if you double the voltage, you would have to put it under twice as much load for it to draw that many amps. So, if you put it under the same amount of load as before (so you go the same speed as before, you accelerate as hard as before), your motor will only be using five amps at the higher voltage.This is because the resistance of the motor didn't change, but the voltage doubled. That means the amount of watts, or power, that the motor has access to is doubled. So, if you double your voltage and don't double your load, you're consuming the same amount of power as before, but at half the current. This results in half the efficiency losses, assuming everything else is equal.But you have an entirely additional range of performance on top of that, which you can access because you've doubled the voltage. So, however fast your bike went before on 100% throttle, it will go that fast at 50% throttle. Then, everything from 50% throttle to 100% throttle will be additional performance. This is, of course, assuming that the controller in question supports that voltage range.<h1>Efficiency Analysis</h1>Let's talk about efficiency. Here, we have a typical 36 volt lithium ion battery with a standard nickel construction using mid-grade cells. This particular battery has a resistance of 95 milliohms. As you can see from the chart, it can output almost 40 amps before it dips below 90% efficiency. That gray dotted line is the expected power—that is, if you just take volts and multiply by amps, but that's only the power you would get in a perfect world.<figure data-trix-attachment="{&quot;contentType&quot;:&quot;image&quot;,&quot;height&quot;:517,&quot;url&quot;:&quot;https://lh7-rt.googleusercontent.com/docsz/AD_4nXdZP9IAu3znpkEajPATHkNKeQd6gIA9n_VJru1zCOy74qVci01mJeK9hMzq3EW46clqNH5pZRm479BE6-PrAYg3vnncBirrUT13PCM0BOFANBV3xXbH36pcCKHM3Bc5GhZZnIGm?key=4dwnAOlJ10o11Sm5BbGD6NOO&quot;,&quot;width&quot;:624}" data-trix-content-type="image" class="attachment attachment--preview"><img src="https://lh7-rt.googleusercontent.com/docsz/AD_4nXdZP9IAu3znpkEajPATHkNKeQd6gIA9n_VJru1zCOy74qVci01mJeK9hMzq3EW46clqNH5pZRm479BE6-PrAYg3vnncBirrUT13PCM0BOFANBV3xXbH36pcCKHM3Bc5GhZZnIGm?key=4dwnAOlJ10o11Sm5BbGD6NOO" width="624" height="517"><figcaption class="attachment__caption"></figcaption></figure>We live in the real world, where every part of the system has resistance, and it all adds up to a sum total resistance. Because its resistance is 95 milliohms, this battery can stay within 10% of the expected power up until that line turns red. After the line turns red, that's when it deviates more than 10% from the expected power, meaning it's less than 90% efficient.So, as long as you run this battery at about 40 amps or less, you won't have any problem with it. At that current level, it can be considered a decent battery because it will probably be reliable at those currents, and it won't overheat or cause any fires. But if you look, you're still getting a 4-volt drop at 40 amps. That means if your battery is at 36 volts, you're only able to put 32 volts of power down. But that's okay—it's still a decent battery.Now, what happens if we build a battery exactly like that, but we change absolutely nothing: we keep the same cells, the same layout, and everything—the same series conductors—and we just extend that further 10 more groups to make a 72 volt battery. What would happen? Well, isn't that interesting? It seems like we haven't improved the efficiency at all. Look: it still deviates 10% from expected power right before 40 amps, and you still drop to about 90% efficiency at 40 amps.<figure data-trix-attachment="{&quot;contentType&quot;:&quot;image&quot;,&quot;height&quot;:517,&quot;url&quot;:&quot;https://lh7-rt.googleusercontent.com/docsz/AD_4nXe3FHGr-7EiSwDCdUgC0ywGmywvt2J4A1OzaDYIMQfXUJq36OjLE_WlSo6CGXbtbEW2xl6hRJ3UOkvskAbAy5QysCy5XCY7hQjUYN8KyHULguQ1JPJMzAJMak5N29o0oQbUpSHf?key=4dwnAOlJ10o11Sm5BbGD6NOO&quot;,&quot;width&quot;:624}" data-trix-content-type="image" class="attachment attachment--preview"><img src="https://lh7-rt.googleusercontent.com/docsz/AD_4nXe3FHGr-7EiSwDCdUgC0ywGmywvt2J4A1OzaDYIMQfXUJq36OjLE_WlSo6CGXbtbEW2xl6hRJ3UOkvskAbAy5QysCy5XCY7hQjUYN8KyHULguQ1JPJMzAJMak5N29o0oQbUpSHf?key=4dwnAOlJ10o11Sm5BbGD6NOO" width="624" height="517"><figcaption class="attachment__caption"></figcaption></figure>But because the voltage is doubled for each amp, we have twice as many watts. If we put both of these batteries on the same chart and follow their paths out to that 10% cutoff point and compare them side by side, it becomes clear that a 72 volt battery is about 5% more efficient than a 36 volt battery at the same load.<figure data-trix-attachment="{&quot;contentType&quot;:&quot;image&quot;,&quot;height&quot;:397,&quot;url&quot;:&quot;https://lh7-rt.googleusercontent.com/docsz/AD_4nXcgxmlsDom6eS7uMNMpre4-2BpDjlRBtah7HEBpOr0XHzhFEpUznvk3WBrhwh-41nccDq4_cwwD-ZTD_-y1GsCI1Qq8mMjDxninE9zajdNLMOUDTtC68fzeMJLN_jFbVJoDP36elA?key=4dwnAOlJ10o11Sm5BbGD6NOO&quot;,&quot;width&quot;:624}" data-trix-content-type="image" class="attachment attachment--preview"><img src="https://lh7-rt.googleusercontent.com/docsz/AD_4nXcgxmlsDom6eS7uMNMpre4-2BpDjlRBtah7HEBpOr0XHzhFEpUznvk3WBrhwh-41nccDq4_cwwD-ZTD_-y1GsCI1Qq8mMjDxninE9zajdNLMOUDTtC68fzeMJLN_jFbVJoDP36elA?key=4dwnAOlJ10o11Sm5BbGD6NOO" width="624" height="397"><figcaption class="attachment__caption"></figcaption></figure>It takes a certain amount of watts to move your bike a mile. It's different for every bike, but it takes a certain amount of watts to move your bike a mile. That means if you get 30 watts per mile and you have a 60 watt charger, then you can charge it 2 miles per hour. You're getting 2 miles of ride time per hour of charge time.<figure data-trix-attachment="{&quot;contentType&quot;:&quot;image&quot;,&quot;height&quot;:404,&quot;url&quot;:&quot;https://lh7-rt.googleusercontent.com/docsz/AD_4nXcGy9GqUsf1o6XMHR_gc-g9PBvuXB98bf89xipM5NIlDY5TsSF6Khq5uBNXwMRkX3lz_MSq4dX1bQyNsQad5wcjmkDF7BQjcFKd6YGLVXLhYKigR1Rk2iaJSPfeHSyqH6AfIKh-?key=4dwnAOlJ10o11Sm5BbGD6NOO&quot;,&quot;width&quot;:624}" data-trix-content-type="image" class="attachment attachment--preview"><img src="https://lh7-rt.googleusercontent.com/docsz/AD_4nXcGy9GqUsf1o6XMHR_gc-g9PBvuXB98bf89xipM5NIlDY5TsSF6Khq5uBNXwMRkX3lz_MSq4dX1bQyNsQad5wcjmkDF7BQjcFKd6YGLVXLhYKigR1Rk2iaJSPfeHSyqH6AfIKh-?key=4dwnAOlJ10o11Sm5BbGD6NOO" width="624" height="404"><figcaption class="attachment__caption"></figcaption></figure>Charging Benefits Of A 72V BatteryBecause the voltage is double, if you compare two otherwise equal 5 amp chargers, you're getting 355.2 watts into your battery for those 5 amps, compared to the 36 volt battery where you're only getting 177.6 watts. Of course, you're consuming more power from your utility company in doing so—you're not getting some magical benefit. It just so happens that the voltage is double and the current is still 5 amps.<figure data-trix-attachment="{&quot;contentType&quot;:&quot;image&quot;,&quot;height&quot;:425,&quot;url&quot;:&quot;https://lh7-rt.googleusercontent.com/docsz/AD_4nXfxOK_TnQYcMXQFwm3RsGo4o913A79DDjEDF2P8Tyx7xrPkBmEHLmSxGTNadAr30v6lejlIIfSGKbeyIAqxb38RNpju8vbmcTPdSMC04PY6ZnRCsFbJdzehxHw1pkwmCGOOhct0eg?key=4dwnAOlJ10o11Sm5BbGD6NOO&quot;,&quot;width&quot;:624}" data-trix-content-type="image" class="attachment attachment--preview"><img src="https://lh7-rt.googleusercontent.com/docsz/AD_4nXfxOK_TnQYcMXQFwm3RsGo4o913A79DDjEDF2P8Tyx7xrPkBmEHLmSxGTNadAr30v6lejlIIfSGKbeyIAqxb38RNpju8vbmcTPdSMC04PY6ZnRCsFbJdzehxHw1pkwmCGOOhct0eg?key=4dwnAOlJ10o11Sm5BbGD6NOO" width="624" height="425"><figcaption class="attachment__caption"></figcaption></figure> You're getting more charge time for the amount of current that you're putting your battery under in terms of stressing it from charging it. Again, when you charge a 72 volt battery, you're doing half of the charging damage you would normally do per mile compared to a 36 volt battery.So, what have we learned? A 72 volt battery is defined by its nominal voltage rather than an absolute, fixed voltage. Whether you're dealing with an NMC battery made of 20 cell groups in series or an LFP battery made of 23 groups, the result is a system that offers a broader voltage range, enhanced performance, and improved efficiency. A higher voltage system not only doubles the available power per amp but also reduces current draw at the same power level as before, which in turn minimizes efficiency losses and charging stress. However, when combining batteries—like linking two 36 volt batteries in series—you have to be careful because of the BMS MOSFETs voltage rating. Ultimately, 72 volt batteries provide more power and are more efficient than an otherwise equal lower voltage setup.&nbsp;

72 Volt Battery

Lets investigate the effects of resistance in series conductors on lithium ion battery packs!

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