How long will your battery last?
Enter your battery capacity and power use to estimate runtime.
Battery runtime
- Available energy
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- Battery power draw
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An estimate for your inputs. Actual performance depends on temperature, battery condition and changing loads.
Capacity alone does not establish compatibility. Check battery voltage, battery and BMS current limits, startup loads and inverter specifications.
How we calculate
First, we convert capacity to watt-hours if needed. Then we account for available energy and the power drawn from the battery.
Runtime (h) = capacity (Wh) × usable fraction ÷ (load (W) ÷ efficiency + inverter idle power (W))Example: a 2048 Wh battery, 200 W load, 90% usable capacity, 90% efficiency and 10 W idle power. Estimate: 2048 × 0.9 ÷ (200 ÷ 0.9 + 10) ≈ 7.94 hours.
Percentages in the formulas are decimal fractions: 90% = 0.9. Energy (Wh) = capacity (Ah) × nominal voltage (V).
Sources & assumptions
These formulas estimate energy. Efficiency, usable capacity and power consumption are user inputs, not specifications of a particular model.
- Victron Energy — battery system design and BMS selection
- Victron Energy — battery monitoring and energy measurement
Methodology updated October 6, 2026
Common questions
Why do I need voltage when entering amp-hours?
Energy depends on voltage: Wh = Ah × V. A 100 Ah battery at 12.8 V stores 1280 Wh, while a 100 Ah battery at 51.2 V stores 5120 Wh of nominal energy.
How do I calculate power station runtime?
Select Wh or kWh and enter the rated battery energy. Allow for conversion losses when using AC outlets. If entering measured usable AC output energy, use 100% efficiency, 100% usable capacity and 0 W idle consumption.
Why can actual runtime differ?
Loads vary, efficiency changes with load, and battery performance depends on temperature, age and discharge current. This simple model may overestimate lead-acid runtime at high discharge rates.