Backup time
14.57hours
Estimated runtime based on average compressor cycling.
Refrigerator Backup Time Calculator
Estimate how long a battery or portable power station may run a refrigerator or freezer during an outage.
Refrigerator compressors cycle on and off, so this estimate uses running watts and duty cycle to calculate average power. It is an electrical runtime estimate only and does not determine whether food is safe to eat.
Refrigerator backup inputs
Wh
Use the battery or power station capacity in watt-hours.
W
Use the compressor running watts from the appliance label or manual.
W
Used as a startup surge note, not as continuous power.
%
Allowed range is 10% to 80%; 35% is a common planning default.
%
Estimated conversion efficiency when powering the fridge from AC output.
%
Energy kept unused so the plan does not rely on fully draining the battery.
Results
Backup time
0.61days
Average load
53W
Running watts multiplied by duty cycle.
Usable battery energy
765Wh
Starting watts
1,200W
Short compressor surge note, not continuous use.
Calculation breakdown
| Item | Value | Notes |
|---|---|---|
| Rated battery capacity | 1,000 Wh | Energy before inverter efficiency and reserve. |
| Average refrigerator load | 53 W | 150 W running x 35% duty cycle. |
| Usable battery energy | 765 Wh | Capacity after efficiency loss and reserve. |
| Runtime | 14.57 hours | 765 Wh / 53 W average load. |
| Starting watts note | 1,200 W | Starting watts are used as a compressor surge note, not as continuous consumption. |
| Food safety caution | Not guaranteed | This estimates electrical runtime only and does not guarantee refrigerated food safety. |
Formula
runtimeHours = capacityWh x (efficiencyPercent / 100) x (1 - reservePercent / 100) / (runningWatts x dutyCyclePercent / 100)Starting watts are included as a surge note because compressor startup can be much higher than running watts, but they are not used as continuous energy consumption.
- capacityWh
- The battery or power station capacity in watt-hours.
- runningWatts
- The refrigerator compressor load while running.
- dutyCyclePercent
- The percentage of time the compressor is expected to run.
- reservePercent
- Battery energy kept unused for planning margin.
Example
A warmer room, frequent door openings, or a freezer pulling down from a higher temperature can increase duty cycle and shorten the estimate.
- Battery capacity is 1,000 Wh.
- The refrigerator uses 150 W while running.
- A 35% duty cycle gives an average load of 52.5 W.
- With 85% inverter efficiency and 10% reserve, usable energy is 765 Wh.
- 765 Wh divided by 52.5 W gives about 14.6 hours of estimated backup time.
How to use this calculator
- Enter battery capacity in watt-hours.
- Enter the refrigerator running watts and optional starting watts from the label or manual.
- Choose a duty cycle between 10% and 80% based on conditions or measured usage.
- Review the runtime estimate alongside the food safety caution and equipment limits.
Input guide
- Battery capacity: stored energy before inverter losses and reserve.
- Running watts: compressor wattage while the refrigerator or freezer is actively running.
- Starting watts: short startup surge used to check whether the power source can start the compressor.
- Duty cycle: estimated percentage of time the compressor runs during the outage.
- Inverter efficiency and reserve: planning assumptions that reduce usable watt-hours.
Common mistakes
- Using starting watts as if the compressor runs at that level continuously.
- Assuming the same duty cycle in every room temperature and season.
- Ignoring battery reserve, inverter loss, or power station output limits.
- Treating an electrical runtime estimate as a food safety determination.
Limitations
This calculator uses a simple average-load model. It does not model thermostat behavior, door openings, food mass, room temperature, defrost cycles, appliance age, inverter surge capability, or battery performance in cold or hot conditions.
FAQ
Why use duty cycle instead of running watts only?
Most refrigerators cycle on and off, so average power over time is usually lower than compressor running watts.
Does this tell me whether food is safe?
No. It only estimates electrical runtime. Food safety depends on temperature history, door openings, appliance condition, and official safety guidance.
What duty cycle should I use?
Use the appliance manual or measured data if available. Without better data, 35% is a planning default, but hot rooms, frequent door openings, and warm food can raise it.
Do starting watts reduce the runtime estimate?
No. Starting watts are shown as a compressor surge note. Runtime uses average watts from running watts and duty cycle.
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Methodology and disclaimer
This tool estimates power runtime only. It does not guarantee food safety. Follow local food safety guidance, appliance instructions, and safe handling practices during outages.
The calculator multiplies running watts by duty cycle to estimate average watts, reduces battery capacity by inverter efficiency and reserve, then divides usable watt-hours by average watts.