Battery runtime calculator
Runtime is capacity divided by current, discounted for how much of the battery you are willing to use and how efficiently it discharges.
Ah
V
%
%
Runtime
3.456hours
- Runtime
- 3:27:22
- Usable energy
- 864.0 Wh
- Nominal energy
- 1200.0 Wh
- Battery current
- 23.15 A
- Discharge C-rate Above 1C many chemistries lose usable capacity.
- 0.2315
- Runtime in minutes
- 207.4
Show the working
- Battery capacity = 100
- Nominal voltage = 12
- Load = 250
- Usable depth of discharge = 80
- Inverter or converter efficiency = 90
- Nominal energy = 100 * 12 = 1200
- Usable energy = 1200 * 80/100 * 90/100 = 864
- Runtime = 864 / 250 = 3.456
- Runtime in minutes = 3.456 * 60 = 207.36
- Battery current = 250 / 12 / (90/100) = 23.1481
- Discharge C-rate = 100 > 0 ? 23.1481 / 100 : 0 = 0.231 481
- Runtime = 3.456 * 3600 = 12 441.6
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- energy = capacity in Ah x voltage
- runtime = usable energy / load power
- C-rate = discharge current / capacity in Ah
Lead-acid should not go below about 50% depth of discharge if you want it to last; lithium iron phosphate is happy at 80 to 90%.
Peukert effect means a lead-acid battery delivers noticeably less than its rated capacity at high currents. This calculator does not model it.