Nameplate kilowatt-hours are not all available—depth of discharge sets the usable floor. This guide walks through the battery DoD to usable energy calculator: nominal capacity in kWh, DoD %, and energy your loads can actually draw.
Benefits
- Formula: usable kWh = nominal kWh × (DoD ÷ 100).
- Typical DoD: LiFePO4 80–90%, lead-acid ~50%.
- Outputs usable kWh, Wh, and reserved capacity in one run.
How it works
- Enter nominal battery capacity in kWh from spec or sticker.
- Set depth of discharge %—chemistry guideline or BMS cutoff policy.
- Read usable energy in kWh and Wh; compare to backup load budgets.
FAQ
How do I calculate usable energy from DoD?
Usable kWh = nominal kWh × (DoD ÷ 100). Example: 13.5 kWh Powerwall-class nominal at 90% DoD → 13.5 × 0.9 = 12.15 kWh usable. The remaining 10% is reserve held by the BMS.
What DoD should I use for lithium vs. lead-acid?
LiFePO4 home storage often plans 80–90% daily DoD for cycle life balance. Flooded or AGM lead-acid is commonly limited to ~50% for longevity. Enter the DoD your warranty and BMS allow—not 100% unless the spec explicitly supports it.
Is usable energy the same as nameplate kWh?
No—marketing kWh is nominal nameplate energy. Usable kWh is what you can discharge to your chosen floor. Runtime and critical-load math must use usable kWh, or you will overestimate backup hours.
Technical specifications
- Usable kWh = nominal_kWh × (DoD% ÷ 100).
- Usable Wh = usable_kWh × 1,000.
- Reserve kWh = nominal − usable.
- Related: battery-dod-energy-yield, battery-depth-of-discharge, ah-to-wh.