# Depth of discharge

Depth of Discharge (DoD) is the fraction or percentage of the capacity which has been removed from the fully charged battery. It is an alternative method to indicate a battery's State of Charge (SoC). The Depth of Discharge is the complement of State of Charge: as one increases, the other decreases.

While the State of Charge (SoC) is usually expressed using percentage points (0% = empty; 100% = full), Depth of Discharge (DoD) is usually expressed using units of Ah (e.g, 0 is full and 50 A h is empty) or percentage points (100% is empty and 0% is full). The capacity of a battery may be higher than its nominal rating. Thus it is possible for the depth of discharge value to exceed the nominal value (e.g., 55 A h for a 50 A h battery, or 110%).

At least in some battery technologies, such as lead-acid AGM batteries, there is a correlation between the depth of discharge and the cycle life of the battery. Depth of Discharge is defined as the capacity that is discharged from a fully charged battery, divided by battery nominal capacity. Depth of discharge is normally expressed as a percentage. For, example, if a 100 A h battery is discharged for 20 minutes at a current of 50 A, the depth of discharge is 50 * 20 / 60 / 100 = 16.7 %.