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    Everyone knows that it's better to build a lithium ion battery with copper. There are so many benefits to using copper. Copper has 4.16 times lower resistance than nickel. Copper is 4.4 times as thermally conductive as nickel. But really, how much better is a copper battery compared to a nickel battery. 

    What specific things about a copper battery are better than a nickel battery? Will it perform better under load? Will I feel additional power and acceleration as a result of using copper? Will my battery have a higher range if I build it with copper? Will my copper battery be able to endure more charge and discharge cycles than my nickel battery?

    In this deep dive article we are going to examine all of these things and give you the exact specific answers that you need to be more empowered as a battery builder.

    Spoiler alert: The reason why we're using such a ridiculous battery as this example is because that's what's required to even be able to produce a difference between copper and nickel worth discussing. This boils down to the fact that series conductors have a stunningly low resistance compared to cells and other ohmic losses. 

    The Example Battery.

    Cells: EVE 40PL 20S4P

    Series Conductor A: 8mm x 0.15mm pure nickel - 4 Links

    Series Conductor B: 8mm x 0.15mm pure copper - 4 Links

    BMS: JK 100A

    Load Range: 0A - 100A 

    How Is This A Ridiculous Battery?

    The battery is ridiculous for several reasons. E40PL cells have extremely low resistance. It's just 3 milliohms. That is so hard to believe that before starting this article, I had to contact a trusted battery cell expert friend of mine and ask him if that was actually the real resistance, and he confirmed that it was. Thanks, Nelvick. 

    The ridiculous part is using these batteries in a 4P configuration with just 4x 8mm links to connect the series groups. Nobody is realistically going to do that. Yes, using four simple links is very common, but the common batteries that are built using that construction method do not have cells like these.

    They don't have cells anywhere near these. The resistance of the batteries that are built with this construction method is somewhere around 20 to 35 milliohms because these are going to be low quality, standard issue 18650 cells. Sometimes they'll be 21700. You might see a MalaCell P42A or something in there every once in a while. But ultimately, you have 20 or 30 milliohms of resistance per cell. And most batteries you're not drawing 100 amps from. Most batteries, even good batteries that you can get a lot of power from, you're drawing 40 to 60 amps from those batteries.

    But a battery like that, even a high performance battery, won't be able to show any difference between copper and nickel. So we need to build this super ridiculous scenario so we can show the difference between the two more effectively.

    How Much Power Is Lost In The Cells?

    EVE 40PL 21700 Battery cells use an NMC chemistry and a tabless design, resulting in a comically low resistance of just 3mOhms. For a 4P battery, we need to divide the resistance by 4 to find the resistance of each cell group. This comes out to 750 microOhms. That is a very low resistance battery cell group for sure, but now we have to put 20 of those in series, which results in 15mOhms. 

    The low resistance of these cells is simply amazing. After adding them all up, the total resistance of the battery pack is less than the resistance of most individual mid range battery cells. That is definitely impressive. But they aren't super conducting, so while the resistance is very low, it's not zero. That means some amount of power will be lost. But how much?

    This alone is super impressive. At 100 amps, so 7.2 kilowatts, the entire battery pack is only losing 150 watts to heat. That is absolutely insane. But that's not the entire story for the cells. As it turns out, lithium ion cells run better when they are hot. Not just a little better, but a lot better. 


    At any appreciable current, the heating inside of the cell happens nearly instantly, in less than a second. It may seem like it takes some time for the batteries to get hot, but that's simply because it takes some time for the cell to saturate with heat enough for it to make its way to the surface, where you can feel it. If you pull a heavy current from a cell for any amount of time, it instantly heats to these temperatures in the core of the chemistry, where it matters. So essentially, in the context of electric vehicles, right away, as soon as you start using your battery in any kind of way in which performance is going to matter, it warms up and its resistance drops by a significant margin. 

    This effect varies cell model to cell model, as there are many factors involved, but most experiments result in a 40% to 60% resistance reduction when comparing room temperature to 60C. For this article, we will use the low end of that. 

    How Much Power Is Lost In The Nickel?

    To know how much power is lost in the series conductor, we must first learn how to properly measure the effective distance that the current has to travel. This distance is much shorter than you may expect. 

    At first (or even second or third) thought, you may think that you need to calculate the resistance of the series conductor along the path of current using its known material resistance. Sadly, this is only part of the story.