What is a C Rating on RC Batteries?

After seeing some confusion on this topic on Facebook and other social media I thought I'd write this for anyone who wants to find it... No judgement at all if you don't know. When I first saw a C rating I had no idea what it meant either.

The C rating of a battery pack is the potential power delivery to the ESC, motor, radio and servo(s). It's not a straightforward number though. Two batteries with a 30C rating may not necessarily be equal. If they have different capacities then the actual power delivery could be quite different.

The maths is thankfully quite simple, but I'm going to start at the very most basic level just to make sure everyone is in the same starting point. Almost all batteries are measured in mAh, and the numbers are often in the 1000's but we can simplify the number. The m before the Ah is for milli which means "1000th of", in this case, an Amp hour* . So 4000mAh is actually just 4Ah. This in turn means the battery can supply 4 Amps for an hour. And that is what 1C means. 

1C is equal to the listed capacity of the battery in Amps So in our 4000mAh example we get 4 Amps.

10C is simply 10 times that. So in our 4000mAh battery we get 40 Amps

100C would be 400 Amps !

This is typically the range of the common batteries for RC cars, with 100C and up being really up at the top end of the scale racing grade LiPo batteries, and 10C being the lowly NiMh.

Here are a couple of typical examples:

This Absima 4200mAh NiMh battery is rated at 10C. Meaning that it can deliver 42 Amps to your motor. Some batteries offer two C ratings, one for constant and another for peak-burst output. This one may also go a little higher for short bursts of acceleration. Solid for your stock "silver can" motors, but may not quite push the most out of upgraded motors as they'll end up current starved.

This Core RC 4000mAh LiPo is rated for 30C / 60C which tells us that it can maintain 30C, but can do bursts of 60C for acceleration. 30C is 120A and 60C is 240A which is more than excess for a brushed motor setup and ESC and probably plenty for most mid powered brushless systems. This particular one is great for vintage 1/10 cars as it is exactly the same dimensions as the old NiCad's that used to come with Tamiya's and a number of other cars.

*Almost all Amps are measured in Amp Hours so to simplify things most manufacturers just write Amps