Depth of Discharge (DoD)
Depth of discharge (DoD) describes how much of a battery's stated charge range has been used, either at a point in time or during a charge-discharge cycle.
Two related uses
Instantaneous DoD is often treated as the complement of State of Charge (SoC): a battery at 70% SoC has 30% DoD when both percentages use the same reference range. This convention must be stated because a vehicle's displayed window can differ from the cell or pack limits used in engineering data.
Cycle depth describes the span covered by one cycle. Moving from 80% to 30% SoC is a 50-percentage-point cycle depth, regardless of where that window sits. It does not mean the battery reached 50% instantaneous DoD at every point in the cycle.
Deeper cycles generally place more stress on lithium-ion cells, but battery aging also depends on temperature, charge rate, time at high or low SoC, chemistry, and total energy throughput. DoD therefore cannot predict service life by itself.
For the detailed aging mechanisms and operating limits, see Battery Degradation.