Nominal Capacity and Battery Aging

Nominal capacity as specified by the battery manufacturer

The nominal capacity is specified by the battery manufacturer as being the amount of energy that can be drawn from the battery over a specified discharging period. If, for example, a current of 20 A can be drawn from a fully charged battery for ten hours, then this battery has a nominal capacity of 200 Ah. Because of the ten-hour discharge duration, the specification of the nominal capacity of 200 Ah must be accompanied by the suffix C10.

In order to be able to compare the nominal capacity of different batteries meaningfully, the nominal capacity of each battery must be based on the same discharge duration (see battery manufacturer documentation).

The usable capacity of a new battery corresponds to the nominal capacity, specified by the manufacturer, for a ten-hour electric discharge (C10). As the battery ages, its usable capacity drops due to the following reasons:

• Calendrical aging

  The usable battery capacity drops over time (even if the battery is not used).

• Cycling

  The battery ages through use. This aging is mainly influenced by the depth of the discharge cycles.

Battery aging is also influenced by various other factors, e.g. by insufficient charging, excessive charging voltages, deep discharges and temperature. With the correct choice of the battery parameters, the battery management system can influence these factors and conserve the battery.