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.
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.
How to Use the Result in the Real World
Treat the calculated result as a planning baseline rather than an exact promise. Real systems lose energy through conversion, wiring, temperature effects and internal electronics, while appliances can draw differently from their nameplate ratings.
Leave practical headroom instead of selecting equipment that exactly matches the result. Extra margin helps with startup surges, battery aging, changing weather and future loads, and it reduces the chance that normal variation pushes the system beyond its limits.
When the result affects a major purchase, verify the important inputs. Measure appliance consumption when possible, check the exact inverter or charge-controller limits, and compare the calculation with the equipment manufacturer's specifications.
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.