Battery Capacity Calculator
Size a battery bank in amp-hours for a required load, runtime and depth of discharge.
About Battery Capacity Calculator
Usable energy is only a fraction of nameplate capacity, because deep discharge shortens battery life sharply. Dividing by both inverter efficiency and depth of discharge gives the nominal capacity that must actually be bought. Lead-acid batteries are normally limited to 50 per cent depth of discharge and lithium to 80 to 90 per cent, which is why the chemistry changes the required capacity so much.
Formula
Battery Capacity
Ah = load × hours ÷ (inverter efficiency × depth of discharge × system voltage)
- depth of discharge
- Share of nominal capacity you are willing to use
- nominal energy
- Total battery energy before the discharge limit is applied
Worked example
With the default values below, Battery Capacity Calculator returns Battery Capacity Required of 113.22. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Loadminimum 0 W
- 500 W
- Required runtimeminimum 0 h
- 8 h
- System voltageminimum 1 V
- 48 V
- Usable depth of dischargeaccepts 0–100 %
- 80 %
- Inverter efficiencyaccepts 0–100 %
- 92 %
Results
- Battery Capacity Required
- 113.22 Ah
- Usable Energy Required
- 4,347.83 Wh
- Nominal Battery Energy
- 5,434.78 Wh
- Nominal Battery Energy
- 5.4348 kWh
- Discharge Current
- 11.323 A
Step by step
- 1Values used
- 2Battery Capacity
- 3Battery Capacity Required= 113.22 Ah
- 4Usable Energy Required= 4,347.83 Wh
- 5Nominal Battery Energy= 5,434.78 Wh
- 6Nominal Battery Energy= 5.4348 kWh
- 7Discharge Current= 11.323 A
Assumptions and limits
- The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax or compounding frequency into account.
- Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Battery Capacity calculated?
Ah = load × hours ÷ (inverter efficiency × depth of discharge × system voltage) Usable energy is only a fraction of nameplate capacity, because deep discharge shortens battery life sharply. Dividing by both inverter efficiency and depth of discharge gives the nominal capacity that must actually be bought.
Why does Battery Capacity matter?
Lead-acid batteries are normally limited to 50 per cent depth of discharge and lithium to 80 to 90 per cent, which is why the chemistry changes the required capacity so much.
What values do I need to enter?
This calculator takes 5 inputs: Load, Required runtime, System voltage, Usable depth of discharge, Inverter efficiency. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.