# The Terminology, Formulae and Physical Assembly of Lipo Batteries - or - Wtf does "C" mean?

It’s the plural of formula

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my life has been forever changed for the better.

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Thank you…that seems to be the perfect start for electric epileptics like me.

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I feel there’s a few things I could have explained better but I can’t edit the post now so hopefully it’s not too bad

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No its not to bad though. I learned a lot from this post, and I know now that my beloved Onan x2 has a 10s2p batterie hahahaha yeah! Feels great to know about that … and i know it has 158wh that means it can reach a distance of almost 16km what is pretty similar to reality…awesome

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sorry Clonkex, the “C” number stands for Coulombs, not Capacity. the “mAh” or “Ah” stands for the Capacity.

Coulombs is the SI unit of 1 amp/sec

So if a battery is rated at 10C with a stated capacity of 5000mAh, the calculation will be 10 x (5000 / 1000) = 50A.

I’m well aware of how the calculation works. If you read the OP you’ll see I do actually explain that.

And unfortunately, you’re wrong. C does in fact stand for capacity. It’s using the standard maths shorthand for multiplication, so 20C is 20 * C, or 20 * capacity. It would make no sense for it to stand for coulombs. 1 coulomb is the amount of charge transported by a constant current of 1 amp for 1 second, so 1 coulomb == 1 amp over 1 second. If the C in 20C stood for Coulombs, that would mean 20amp-seconds (which is nonsensical when it’s used to measure maximum current delivery, and 20A-seconds would be a very small battery, only 5.555mAh), and that would be the same for every battery. In reality the C stands for capacity, so 20C for a 5000mAh battery means that battery can deliver 100 amps nominal, but 20C for an 8000mAh battery allows 160 amps nominal.

But if I got any of that wrong, please correct me

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I guess the C doesn’t refer to either Capacity nor Coulomb. The C rate on the battery stands for the discharge rate. so a 1C means that it can discharge the capacity of the battery within an hour. 10C refers to a tenth of an hour.

Meaning to say that if your battery is rated 5000mAh with 1C, it will discharge the entire capacity of 5000mAh within an hour. if 10C, it will mean that it is capable to discharge 5000mAh in 6mins.

For a battery with a capacity of 100 Amp-hrs, this equates to a discharge current of 100 Amps. A 5C rate for this battery would be 500 Amps, and a C/2 rate would be 50 Amps.

so i guess this clears the teminology behind the C and Capacity. the C is most likely to be described as discharge rate.

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I guess you could read it that way. Personally I think it’s easier to understand as simply meaning capacity since that’s how the formula works, even though I wouldn’t expect C to mean capacity except in the context of defining a discharge rate. Either way we all know the C-rate of a battery is the discharge rate, so I guess it doesn’t matter what C stands for ¯\_(ツ)_/¯

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