100Ah battery runtime
How long will a 100Ah battery run a refrigerator?
A 100Ah label is not enough to predict refrigerator runtime. Battery voltage, chemistry, measured fridge energy, compressor cycling, and inverter loss all change the answer.
Start with watt-hours
A 12V 100Ah battery stores 1,200Wh nominal. A 12.8V LiFePO4 battery stores 1,280Wh. The usable amount is lower after the selected depth of discharge and battery efficiency.
usable Wh = V × Ah × DoD × battery efficiencyUse daily refrigerator energy when possible
A compressor does not run continuously. A 120W nameplate is not the same as a steady 120W load. Measure energy over a representative 24-hour period, or use a documented daily kWh figure. Hot weather, door openings, ventilation, and thermostat settings can change that figure.
Worked planning example
Suppose a 12.8V 100Ah LiFePO4 battery uses an 80% discharge limit and 95% battery efficiency. It provides about 973Wh before AC conversion. With a 90% efficient inverter, about 876Wh reaches the refrigerator. If the refrigerator uses 600Wh per day, the estimate is roughly 35 hours.
runtime days = battery Wh available to the load ÷ refrigerator Wh/dayDC and AC refrigerators differ
A direct DC refrigerator avoids inverter conversion and idle draw. An AC refrigerator needs both included. Startup power also matters for inverter compatibility, but a short startup surge should not be multiplied by the full runtime.
Run your own numbers
Use the battery runtime calculator with a measured average load, or build a refrigerator and essential-load scenario in the battery backup calculator. Treat the result as a planning estimate and keep reserve for temperature and battery aging.