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.[1]


For almost all known rechargeable battery technologies, such as lead-acid batteries of all kinds like AGM, there is a correlation between the depth of discharge and the cycle life of the battery.[2] Depth of discharge is defined as the total amount of energy that is discharged from a battery, divided by the battery nominal capacity. Depth of discharge is normally expressed as a percentage.

While the state of charge is usually expressed using percentage points (0% = empty; 100% = full), depth of discharge is either expressed using units of Ah (e.g. for a 50 Ah battery, 0 Ah is full and 50 Ah 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 Ah for a 50 Ah battery, or 110%).

Sample calculation[edit]

If a 90 Ah battery is discharged for 20 minutes at a constant current of 50 A, the depth of discharge is:

See also[edit]


  1. ^ "The relationship between coefficient of restitution and state of charge of zinc alkaline primary LR6 batteries" (PDF). doi:10.1039/C5TA01576F. Cite journal requires |journal= (help)
  2. ^ discharge characteristics