Depth of discharge
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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 %.