The Battery C-Rate refers to the rate at which a battery is charged or discharged. It is normally expressed in terms numbers that look like 1C, 2C, 0.5C or 0.2C.
The number in these expressions is simply a multiplier.
The letter C in those expressions in more easily understood if you think of it as simply the value of the Amp Hour rating.
In truth, it stands for Coulomb (as in Charles Coulomb), but if you think of it in those terms, you’ll get yourself pretty confused as it really has little to do with the electrical unit known as a coulomb in the context of modern battery discussions.
Like I said, think of C as being the equivalent of the value for the amp hour rating, thus for a 50 Amp Hour battery:
- 1C = 1 x 50 = 50 Amps
- 2C = 2 x 50 = 200 Amps
- 0.5C = 0.5 x 50 = 25 Amps
- 0.1C = 0.1 x 50 = 5 Amps
Put into context of battery manufacturers or engineers speaking of battery performance, you may hear:
“When discharged at 1C, this battery will last 40 minutes. When discharged at .2C, the battery will last of 58 minutes.”
Translation: If this were a 200 amp hour battery, it will last for 40 minutes if discharged at 200 amps and will last for 58 minutes if discharged at a rate of 40 amps.
“This battery is capable of receiving a bulk charge at 2C“
Translation: If this were a 75 amp hour battery, you could apply a bulk charge at a rate of 150 amps.