Best Battery for High-Powered Torches

The best battery for a high-power flash light is the [high end cell here] and the best battery for a mid range flash light is the [mid range cell here]. Lithium-ion 21700 cells that use NMC chemistry have the most power and energy density compared to other flash light batteries. When it comes to finding the best battery for a high-powered flash light, you will need to consider two important factors: capacity and resistance.

How To Pick The Best flash light Battery

You will often find that there is a trade-off between capacity and resistance in a battery cell. For example, you'll find that the highest capacity battery cells, such as a 5000mah to 5800mah 21700 cell, will generally have lower continuous and max current ratings as well because there’s roughly an inversely proportional relationship between the resistance of a battery cell and its capacity.

There's something about how the cells connect on the inside and how they can be packaged that can result in either a very low-resistance connection to the chemistry or lots of room for the chemistry. And it makes sense because it's all about the contact area, right? If you've got more room for very large electrodes that connect to many points or just a large area of the chemistry, then you're going to have less room for the chemistry itself.

So that means there's really no way to overbuy in an attempt to underworry. You have to know how much brightness you need to know how much current you need. Once you know how much current you will need, you have to know how long the flash light can last at that brightness to know how much capacity you need. 

If you try to just buy the highest capacity, lowest-resistance cells, you will run into a problem because like I said, they're usually inversely proportional to some degree. So you kind of have to know which one you need (capacity or ampacity) more than the other so you can optimize your purchasing decision for that use case.

Doing the Math

That means we're going to have to do some math to make any sense of this article. We're going to have to determine how much power a given brightness uses — like the most popular brightness or the most desirable brightness, or two different desirable or popular brightness levels. We have to find out how many watts those things use.

And then we also have to find out how hot, or at least how many waste watts, are going to be generated as a result of the imperfections and resistance in the battery. Once we determine how much power is going to heat as waste, and determine how much power is going to light, then we can determine the ratio between those two. And we can optimize for one or the other.

Flash Light Power Categories

First, let's break this down into three different categories: low end, average, and high power. We'll run the numbers for the average "high brightness" flash lights and also high-end, high power flash lights. We won't spend any time on the lower-end flash lights.

Commodity-level low-end flash lights output somewhere around 200 to 600 lumens. When it comes to "high brightness" flash lights, regardless of what the packaging may claim — and some claim as high as a million lumens — your average low-cost flash light is going to output somewhere between 800 and 1,200 lumens initially.

Then, at the other end of the spectrum, you have those extremely bright flash lights that can throw massive walls of photons for extremely long distances. Those operate at about 2,500 to 5,000 lumens. If you've got 2,500 lumens, you're going to have a very nice, strong, powerful beam.

Example Calculations

We will base these examples on 1,000 lumens and 3,000 lumens.  110 lumens per watt is a good mid-range figure to use for LED efficiency. These flash lights are operating in what's called a 1S configuration because there's not any more than one battery cell, so there cannot be any cells in series. So that means they're operating at the nominal voltage range of 3.7 volts.

Considering these numbers, a mid-range high-brightness flash light will draw about 9 watts (2.46A) from the battery. For one of those extremely bright flash lights that can light up entire fields at 3 a.m., you will draw around 27 watts (7.37A) from the battery cell.

Resistance and Power Loss

For the mid-range flash light that draws just 9 watts, the voltage drop experienced by the 25 milliohm cell is just 0.061 volts. So that means only 0.15 watts is wasted — about 1.7% of the total power is burned off inside the cell as heat. But it's not that big of a deal. But if you use that same cell in the high-brightness flash light that draws 27 watts, the voltage drop becomes 0.184 volts, which burns 1.36 watts internally inside the cell. That's about 5% of the total power, and it'll cause noticeable heating of the cell and a noticeable drop in flash light brightness.

Now let's see what happens with the 4mΩ cell. For the mid-range flash light, we get a voltage drop of just 0.01 volts, which is a power loss of just 0.024 watts — practically nothing at all. And then with the super high power flashlight, we only get a voltage drop of 0.03 volts and an internal power loss of about a fifth of a watt, which is less than 1% of the total output and ultimately completely insignificant.

Factoring In Capacity

But that's just current performance. Once you factor in capacity, you can gain an even greater understanding.

In our example the 25 mAh cell is a 5600 mAh battery. The 4 mAh cell, on the other hand, is 4800 mAh. For the mid-range flash light, the 25 mAh cell can give you about 2.3 hours of run time. But the 4 mAh cell will last about 2 hours, but it will be more efficient while it's doing so — producing less heat internally and providing a stronger beam.

In the high-brightness (27-watt) flash light, the 25 mAh cell only gets 46 minutes of operation, compared to 40 minutes for the lower-resistance cell.

So, low-resistance cells matter way more for high-brightness flashlights. But, at the low end and in the mid-range, you can focus squarely on capacity.

What Does It All Mean?

This clearly highlights the importance of low-resistance cells when using them with flash lights because you want to send as much power as possible to the LED rather than burning it off as heat inside the cell, which only damages the cell over time. On the other hand, it also shows that you can use a higher-resistance cell in a lower-power flash light with absolutely no difference in performance or long-term reliability.

So basically, if you're shopping for battery cells for a flash light and it's for a standard mid-range, high-brightness flash light, then you want to shop based on capacity — you just want to buy as much capacity as you possibly can. But if you are shopping for a battery for one of those extremely high-powered flash lights, then capacity should take a backseat to resistance.

So, What Is The Best Battery For High Power flash lights?

It depends on what you mean by high power. If you're talking about your standard issue, high brightness flash light that can be used to effectively light up a completely dark house so you can find somethin, then that will be [mid range cell here], with its X mOhms of resistance and Y mah of capacity, its more than you will ever need for a flash light like that.

In contrast, if you're talking about a very high end powerful flash light that you would need to light up a massive empty field in the middle of the night, then [high end cell here] would be a much better option, because despite its low capacity, it has the ability to handle the raw power that your flash light demands.