Depth of discharge

Depth of discharge describes how much of a battery’s stored energy has been used from its charged state. In home battery datasheets it is usually a percentage linked to usable capacity: a battery described at 90% depth of discharge gives access to more of its nominal capacity than one limited to 80%. The figure matters because deeper discharges can reduce cycle life, although battery chemistry, temperature and charge or discharge rate also affect ageing. A published 100% depth-of-discharge figure should be read with the usable capacity, retained-capacity warranty and allowed-use conditions for that product rather than as a promise that every full cycle has no effect on battery ageing.