Capacity

A battery's capacity indicates how much electrical charge it can store and release. It is measured in ampere-hours (Ah); for battery storage systems, the storable energy is usually expressed in kilowatt-hours (kWh) or megawatt-hours (MWh). The actual usable capacity may differ from the rated capacity and depends, among other factors, on temperature, charge and discharge rates, and operating limits. It generally decreases as the battery ages and thus serves as an important indicator of the battery’s condition.