Life and ageing
Depth of discharge (DoD)
The fraction of a cell capacity removed during a discharge, expressed as a percentage.
What it changes in practice
Depth of discharge and cycle life are inversely related: shallow cycles cost far less ageing per cycle than deep ones. A pack cycled to 20% DoD will complete many more cycles than the same pack cycled to 90%, which is why storage warranty terms are written against a stated DoD. It also means that cycles alone is not a comparable unit of battery life; energy throughput over life is closer to it.
Why it matters when you specify a cell
Depth of discharge decides how much of the cycle-life figure you can use. Shallow cycling ages cells far more slowly, so a product that runs 100–50% can honestly claim a longer life than one that runs 100–10%. Choose the usable window from the product behaviour, then state it in the specification and the warranty.
Related terms
Read further
More in Life and ageing
Other terms in this group
How cells age, and which numbers describe it honestly.
Cycle life
The number of charge and discharge cycles a cell completes before its capacity falls below a stated fraction of its original value, usually 80%.
Read the entry →State of charge (SoC)
The remaining charge in a cell at a given moment, expressed as a percentage of its current usable capacity.
Read the entry →State of health (SoH)
The current condition of a cell expressed as a percentage of its original capability, usually capacity, sometimes resistance.
Read the entry →Calendar life
Ageing that occurs with time rather than with use, driven mainly by temperature and state of charge during storage.
Read the entry →