Estimate how long a battery will last from battery capacity, voltage, load watts, inverter efficiency, depth of discharge, battery type, and reserve capacity. This calculator is useful for camping, RV solar, backup power, portable power stations, off-grid systems, lights, fans, CPAP machines, fridges, and small electronics.
Battery capacity:
The calculator converts amp-hours, watt-hours, or kilowatt-hours into total watt-hours available from the battery bank.
Usable energy:
Depth of discharge, reserve capacity, battery type, temperature, and battery condition adjust how much of the battery can realistically be used.
Runtime:
Usable watt-hours are divided by the effective load watts to estimate runtime in hours, days, and hours/minutes.
A battery runtime calculator helps estimate how long a battery will power a fridge, fan, light, CPAP, laptop, inverter, RV appliance, solar load, or emergency backup device.
Actual runtime depends on battery age, temperature, discharge rate, inverter idle draw, device cycling, wiring loss, voltage cutoff, and manufacturer ratings.
This calculator uses a practical battery runtime formula:
Runtime Hours = Usable Battery Watt-Hours ÷ Effective Load Watts
Convert the battery to usable watt-hours, then divide by the load watts. For example, a 1200 Wh battery running a 100 W load may last about 12 hours before losses and reserve settings.
It depends on voltage and load. A 12V 100Ah battery has about 1200 Wh total capacity before depth-of-discharge limits, losses, and reserve capacity.
Runtime can be shorter because of inverter losses, cold weather, old batteries, high discharge rates, device startup surges, voltage cutoff, and inaccurate capacity ratings.
Usually yes. AC loads require an inverter, and inverters lose some power while converting DC battery power to AC power.