How Long Will a 100Ah Lithium Battery Run a Refrigerator?
Estimate refrigerator runtime from measured daily kWh instead of multiplying compressor running watts by 24 hours.
Refrigerators cycle. The most accurate way to estimate battery runtime is to measure the appliance over a full day and compare that energy use with usable battery watt-hours.
A 100Ah LiFePO4 battery is usually around 1.28kWh nominal at 12.8V. After inverter losses and reserve, usable AC energy may be closer to roughly 1.0–1.1kWh. Runtime therefore depends mainly on the refrigerator’s measured daily kWh, not its compressor watt rating.
What matters
- Use 24-hour kWh whenever possible.
- Account for inverter conversion losses.
- Compressor startup must fit inverter surge capability.
- Ambient temperature and door openings change consumption.
Decision factors that change the answer
Convert Ah to Wh
Amp-hours are incomplete without voltage. At 12.8V, 100Ah is about 1,280Wh nominal.
Use daily kWh
A refrigerator that consumes 0.8kWh/day can run far longer than one consuming 1.5kWh/day even if their compressors have similar watt labels.
Account for inverter loss
A DC battery powering an AC refrigerator loses energy through the inverter.
Check startup
The inverter and BMS must tolerate compressor startup even when the energy calculation says the battery is large enough.
How to size it
- Measure refrigerator kWh/day.
- Convert the battery to usable Wh.
- Divide usable Wh by the refrigerator daily Wh.
- Verify startup surge separately.
If a refrigerator uses 1kWh/day and the battery system delivers about 1.1kWh usable AC energy, the practical expectation is around one day, not an exact 24-hour guarantee.
Worked example
If the battery provides 1.05kWh of usable AC energy and the refrigerator uses 0.9kWh/day, the arithmetic is about 1.17 days. If the refrigerator uses 1.4kWh/day, runtime drops to about 18 hours. Measured appliance energy is the decisive input.
Common buying mistakes
- Assuming the compressor runs continuously.
- Using only the fridge nameplate current.
- Ignoring inverter idle draw on very efficient refrigerators.
Measure the refrigerator first. Its daily kWh matters far more than a generic fridge wattage estimate.
Check the underlying numbers
Use these site resources to replace generic assumptions with your own load or the source-linked data behind this guide.
Use the numbers before choosing a model
Start with your load list. The battery needs enough watt-hours for the desired runtime and enough continuous/surge watts to operate the appliances at the same time. Then check whether your recharge method can replace the energy you expect to consume.
For outage planning, we recommend keeping reserve capacity instead of designing a system that reaches 0% at the end of the forecasted outage.
Next step
Estimate battery runtime → or Build a critical-load energy budget →.