Battery Capacity Calculator
Calculate required battery watt-hours and amp-hours from load, runtime, efficiency, depth of discharge and voltage.
Calculate required battery watt-hours and amp-hours from load, runtime, efficiency, depth of discharge and voltage.
Enter your own equipment values. The calculator uses transparent assumptions so you can adjust efficiency, reserve and operating conditions.
Use Real Equipment Ratings
Calculate required battery watt-hours and amp-hours from load, runtime, efficiency, depth of discharge and voltage.
Calculator Guidance
Use the result for planning, then verify the exact product manual, nameplate ratings and operating limits.
Battery Capacity Calculator
Planning estimate only.
Formula
Required battery Wh = watts × hours ÷ efficiency ÷ usable depth of discharge. Amp-hours = Wh ÷ voltage.
Examples
| Load/Runtime | Efficiency/DoD | Required Wh | Approx. 12.8V Ah |
|---|---|---|---|
| 100W × 10h | 85% / 90% | 1307Wh | 102Ah |
| 500W × 5h | 90% / 90% | 3086Wh | 241Ah |
| 1000W × 4h | 90% / 80% | 5556Wh | 434Ah |
Battery-Sizing Limits
Discharge Current
The battery must supply inverter amps.
Surge
BMS limits apply.
Temperature
Cold reduces capacity.
Aging Margin
Capacity declines with cycles.
Parallel Wiring
Use matched batteries.
Charging Time
Large banks need adequate chargers.
Frequently Asked Questions
Should I size in Wh or Ah?
Wh is better for comparing different voltages.
What depth of discharge should I use?
Use the battery manufacturer’s recommendation.
Why add efficiency losses?
Inverters and wiring consume energy.
Can one battery supply the current?
Check continuous and surge discharge ratings.
Should I add aging margin?
Yes for long-term systems.
Does battery chemistry matter?
Yes.