Depth of discharge

Depth of discharge (DoD) is an important parameter appearing in the context of rechargeable battery operation. Two non-identical definitions can be found in commercial and scientific sources. The depth of discharge is defined as:

1. the maximum fraction of a battery's capacity (given in Ah) which is removed from the charged battery on a regular basis.^[1][2][3][4] "Charged" does not necessarily refer to fully or 100 % charged, but rather to the state of charge (SoC), where the battery charger stops charging, which is achieved by different techniques.
2. the fraction of the battery's capacity which is currently removed from the battery with regard to its (fully) charged state. For fully charged batteries, the depth of discharge is connected to the state of charge by the simple formula ${\displaystyle \mathrm {DoD} =1-\mathrm {SoC} }$. The depth of discharge then is the complement of state of charge: as one increases, the other decreases. This definition is mostly found in scientific sources.^{[5][6][7][8][9]}

The depth of discharge can therefore (1) refer to the size of the range usually used for discharge or (2) the current amount of charge or fraction of the capacity removed from the battery. To avoid confusion, the exact meaning of DoD should be clear for a given context. Also, for both definitions, it remains undefined, whether a charged battery's SoC is 100 % or another value. This reference value is needed to fully describe (1) the upper and lower limit of absolute SoC used for operation or (2) the current value of the absolute SoC.