Battery Runtime & Inverter Size
For power stations, RV and backup battery banks.
Runtime
–
Estimates only. Assumes 85% inverter efficiency. Fridges and pumps cycle on and off, so enter their average draw for runtime and their starting watts for the surge.
Shop by this size
We earn a commission if you buy through these links. Category pages and searches matched to your numbers, not ranked by commission.
How runtime and inverter size are worked out
Power station: runtime = capacity (Wh) × 0.85 ÷ load (W). The 0.85 covers the loss in the built-in inverter, a rule power station makers publish. The station's AC output must cover your running watts and its surge rating your starting watts.
Battery bank: energy (Wh) = amp-hours × volts. You can only use part of it: lead-acid and AGM last far longer if you stop at about 50%, while LiFePO4 is usually rated for 80–100% (check the datasheet). Through an inverter, take off another 15%. Runtime = usable Wh ÷ load W.
Inverter: continuous rating ≥ running watts ÷ 0.8 (so it isn't flat out), surge rating ≥ starting watts. The current the inverter pulls from the battery is watts ÷ (volts × 0.85), which is why 12 V gets impractical above about 2,000 W: cables and fuses get very heavy.
Lead-acid batteries also deliver less than their rating at high currents (the Peukert effect), so treat lead-acid results at big loads as optimistic.
How long will a 1,000 Wh power station run a 100 W load?
About 8.5 hours. Power stations lose roughly 15% converting battery power to AC, so usable energy is about 1,000 × 0.85 = 850 Wh, and 850 ÷ 100 W = 8.5 h.
How long will a 12 V 100 Ah battery last?
A 12 V 100 Ah battery stores 1,200 Wh. A LiFePO4 battery can use nearly all of it: through an inverter at 85% efficiency it runs a 100 W load about 10 hours. A lead-acid or AGM battery should only be drained to about 50%, so the same load runs about 5 hours.
What size inverter do I need?
Pick a continuous rating at least 25% above your running load (running ÷ 0.8) and a surge rating at least equal to your starting watts. For 1,500 W running and 3,000 W starting, that is at least 1,875 W continuous and 3,000 W surge, so a 2,000 W inverter with a 3,000 W or higher surge.
Sources: power station efficiency rule as published by Jackery; depth-of-discharge ranges from battery makers' datasheets.