Depth of discharge (DoD)
The fraction of a battery's capacity that has been discharged, or the maximum fraction a manufacturer allows to be used per cycle.
Depth of discharge is the complement of state of charge: a battery at 30% SoC has a DoD of 70%. On datasheets, DoD usually means the usable share of nominal capacity, which determines how much energy can actually be delivered.
Usable energy (kWh) = nominal capacity (kWh) x allowed DoD
Example: 10 kWh LFP battery at 90% DoD = 9 kWh usable
DoD strongly affects cycle life. Lead-acid batteries are typically limited to 50% DoD; cycling them deeper can cut life to a few hundred cycles. Lithium-ion tolerates 80–100% DoD, though shallow cycling still extends life: an NMC cell rated 1,500 cycles at 100% DoD may deliver several thousand cycles at 50% DoD. A useful comparison metric is total energy throughput (cycles x DoD x capacity), which for modern LFP home batteries is often warranted at 30–40 MWh per 10 kWh unit.
Flow batteries can be cycled at 100% DoD without degradation. When sizing a solar battery, divide the required nightly energy by DoD and by round-trip efficiency to get the nominal capacity needed, as in the solar battery calculator.
Related terms
All terms →- State of charge (SoC)
The remaining charge in a battery expressed as a percentage of its current full capacity.
- Cycle life
The number of full charge-discharge cycles a battery can deliver before its capacity falls to a defined end-of-life threshold, usually 70–80% of rated capacity.
- Lithium-ion battery
A rechargeable battery in which lithium ions shuttle between a graphite anode and a metal-oxide or phosphate cathode; the dominant chemistry for EVs and grid storage.
- Round-trip efficiency
The share of energy put into a storage system that can be recovered on discharge, measured at a defined boundary (cell, DC, or AC grid connection).
- C-rate
The charge or discharge current of a battery relative to its capacity; 1C empties a full battery in one hour, 0.5C in two hours.