# C coefficient (battery)

The C coefficient is a characteristic value about the available nominal capacity ofbatteries and accumulators. It is a measure of the residual capacity during charging and discharging of rechargeable batteries and is directly related to the charging current and the discharging current, i.e. the current that a rechargeable battery or a battery can supply over a certain period of time.

The C coefficient indicates the charge current or discharge current of a battery or accumulator in relation to the total capacity. The C coefficient or C rate represents the rated capacity or the remaining capacity and the time over which the maximum discharge current can be drawn. Discharge can be at a constant current, through a constant resistance, or at a constant power. The C-factor is a dimensionless number given in conjunction with the letter C, for coulomb: 1C, 2C, 20C, etc., or also as C5, C10, and also in fractions such as C/10 or C/2. For example, 1C means that a battery with a rated capacity of 1 ampere-hour( Ah) will provide a discharge current of 1 ampere for one hour. If a battery with the same rated capacity has a C coefficient of 2C, then the discharge current is 2 amps over 30 minutes, and if the coefficient is 0.2C, it has a discharge current of 200 mA over 5 hours.

When the fraction is used, the value refers to the discharge time. Thus, C/10 means a ten-hour discharge current. Instead of the C coefficient, the discharge time is often specified. Thus, instead of 0.2C, one speaks of a 5-hour discharge or, at 0.1C, of a 10-hour discharge. On the other hand, one can also speak of removable capacity in this context. For example, a battery with a nominal capacity of 10 kWh and a C coefficient of C5 has a discharge capacity of 2 kW over 5 hours, which corresponds to an energy throughput of 2 kWh.