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Battery Runtime Calculator

Pick your power station, or enter any battery in watt-hours or amp-hours. Add what you want to run and see how long it lasts. It also checks whether it can handle the startup surge of fridges and pumps.

1Your battery or power station

1,024 Wh · 1,800 W continuous · 3,600 W surge

2What you want to power

  • RefrigeratorFull-size, ENERGY STAR. Cycles on and off: runs about 39% of the time
  • Wi-Fi router + modem
  • Phone chargingUSB
  • LED light bulb60 W equivalent
Settings & assumptions
Share of battery energy that reaches the AC outlets. 85% is typical.
Power the inverter uses just by being on. Matters most for small loads like a router or CPAP.
Running devices at the same time
"One at a time" assumes devices used less than 2 hours a day (microwave, kettle…) aren't switched on together.
0 = no solar. Includes a 25% real-world loss.
About 3 in winter, 5–6 on clear summer days in most of the US.
Estimated runtimeDetails

How the runtime estimate works

The calculator adds up the average power of everything on your list, including how often fridges and freezers cycle on and off. Then it divides the battery's usable energy by that load:

Runtime (hours) = Battery Wh × inverter efficiency ÷ average watts

For a typical ENERGY STAR fridge averaging 58 W on a 1,024 Wh station: 1,024 × 0.85 ÷ 58 ≈ 15 hours. For a battery rated in amp-hours, multiply by its voltage to get watt-hours first: 100 Ah × 12.8 V = 1,280 Wh. If you set hours per day for each device, you also get how many days the battery lasts on that schedule.

It then checks two limits that decide whether the station can run your devices at all: the continuous output (everything running together) and the surge rating (a motor or compressor starting). The full method, with every assumption, is in How we calculate.

Typical runtimes on a 1,000 Wh power station

Nonstop runtime for one device at a time, using typical US wattages from ENERGY STAR, DOE and manufacturer data. Your devices may differ.

Estimated nonstop runtime on a 1,000 Wh power station
DeviceAverage drawRuntimeBar
LED light bulb9 W3.9 days
Phone charging10 W3.8 days
Wi-Fi router + modem15 W2.4 days
CPAP30 W28 hours
Laptop50 W17 hours
Starlink Standard90 W9.4 hours
TV100 W8.5 hours
Chest freezer29 W29 hours
Refrigerator58 W15 hours
Window AC225 W3.8 hours
Microwave1,500 W34 min
Space heater750 W1.1 hours

Questions

How do I calculate how long a power station will last?
Multiply the battery capacity in watt-hours by the inverter efficiency (about 0.85), then divide by the average watts your devices use. A 1,024 Wh station running a 100 W TV lasts about 1,024 × 0.85 ÷ 100 ≈ 8.7 hours.
Why does my power station run out sooner than capacity ÷ watts?
Converting battery power to 120 V AC loses energy (typically 10–15%), the inverter uses some power just by being on, and cold temperatures and battery age reduce usable capacity. This calculator includes inverter losses by default, and you can add idle draw under Settings.
What is the difference between running watts and starting watts?
Devices with motors or compressors, like fridges, pumps and air conditioners, pull several times their running watts for a split second when they start. A power station must handle that surge or it shuts off. More on surge.
How long will a 12 V 100 Ah battery last?
Turn amp-hours into watt-hours first: Wh = Ah × volts. A 12 V 100 Ah lithium (LiFePO4) battery is about 1,280 Wh, since its nominal voltage is 12.8 V. Through an inverter at about 85% efficiency, a 100 W load runs for about 1,280 × 0.85 ÷ 100 ≈ 11 hours. Lead-acid batteries should only be run down to about half, so count half their capacity: about 5.4 hours for the same load. Pick "Other battery" in the calculator and enter Ah and volts to do this for your own battery and devices.
How do I find how many watts my appliance uses?
Check the label on the device or its power adapter (watts, or volts × amps). For fridges and freezers, the yellow EnergyGuide label lists kWh per year: divide by 365 for kWh per day. A plug-in watt meter gives the most accurate number.

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