Depth of Discharge (DoD)
The percentage of a battery's total nominal capacity that has been discharged relative to its overall capacity rating.
Depth of Discharge (DoD) indicates how deeply a battery can be depleted relative to its overall nameplate capacity. For example, if a 10 kilowatt-hour (kWh) battery has delivered 8 kWh of electricity, it has operated at an 80% Depth of Discharge with 20% State of Charge (SoC) remaining.
DoD Across Different Battery Chemistries
- Lithium Iron Phosphate (LFP): Modern residential LFP batteries support 90% to 100% daily DoD with minimal capacity loss over thousands of cycles.
- Nickel Manganese Cobalt (NMC): Residential NMC batteries are typically calibrated to 80%–90% DoD to preserve cathode stability and prevent accelerated cell aging.
- Traditional Lead-Acid (AGM/Gel): Lead-acid deep cycle batteries should rarely exceed 50% DoD. Depleting lead-acid past 50% damages plates and cuts cycle life in half.
Usable Capacity vs. Nameplate Capacity
When sizing home backup power, always calculate backup runtime based on usable capacity (total capacity multiplied by rated DoD) rather than gross nameplate storage. Quality manufacturers explicitly publish usable energy in kilowatt-hours.
Why it matters
Depth of Discharge directly dictates usable backup runtime during power outages. A battery with higher allowable DoD provides more usable electricity per dollar without risking cell degradation.
Example
A 13.5 kWh battery rated at 100% DoD provides 13.5 kWh of usable backup energy, whereas an older 10 kWh lead-acid bank rated at 50% DoD yields only 5.0 kWh of usable energy before requiring grid or generator recharge.