Battery Runtime Calculator
Estimate how long a battery or portable power station will run a given load, accounting for battery chemistry and inverter efficiency.
Most portable power stations and modern caravan/RV batteries use LiFePO4. It tolerates near-full discharge, so usable capacity is close to rated capacity.
Estimated Runtime
Rated capacity
1 kWh
Estimated usable capacity
950 Wh
95% of rated (chemistry-based)
Estimated runtime
13.5 hours
Runtime = usable capacity ÷ effective load. Usable capacity = rated capacity × typical depth of discharge for LiFePO4 (Lithium Iron Phosphate) (95%). Effective load = 60W ÷ 85% efficiency, to approximate inverter losses.
How runtime is calculated
Runtime depends on usable capacity, not just the rated Wh printed on the box. LiFePO4 batteries can typically be discharged much further than lead-acid types before damage occurs, so their usable capacity is much closer to their rated capacity. AC loads also lose some energy in the inverter's DC-to-AC conversion, so we divide the load by your efficiency setting to estimate the real draw on the battery.
Worked example
A 1,000Wh LiFePO4 power station (95% usable ≈ 950Wh) running a 60W AC load at 85% efficiency draws about 60 ÷ 0.85 ≈ 70.6W from the battery. Runtime ≈ 950 ÷ 70.6 ≈ 13.5 hours.
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Frequently Asked Questions
Why is my usable capacity less than the rated capacity?+
Most batteries aren't fully discharged in practice — either the chemistry doesn't tolerate it well (lead-acid), or the manufacturer's battery management system reserves a margin. LiFePO4 typically allows a much deeper discharge than AGM, gel or flooded lead-acid.
Does inverter efficiency really matter that much?+
Yes — a 15% loss compounds over hours of use. Running AC appliances directly from 12V where possible (e.g. a 12V fridge instead of an AC one) avoids this loss entirely.
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