How long will a power station last in an outage?
Updated
The formula
Runtime in hours = rated capacity × 0.85 ÷ watt hours a day × 24. The 0.85 is the share of the rating that reaches the outlets after the inverter. Watt hours a day come from each appliance: running watts × the hours it runs, or the daily energy figure for a refrigerator or freezer, whose compressor rests part of each hour.
For a 2,000 Wh station and the outage essentials: 2,000 Wh × 0.85 = 1,700 Wh, divided by 2,180 Wh a day, times 24 = 18.7 h. The result is calendar time while you follow the same routine every day, with use spread through the day.
Runtimes by size
Battery math only, at the nominal sizes. A real station also has to pass the output and surge checks for the list, which each station page and setup page does.
| Capacity | Usable | Refrigerator, 1,300 Wh a day | CPAP, 88 Wh a night | Outage essentials, 2,180 Wh a day | Router only, 672 Wh a day |
|---|---|---|---|---|---|
| 500 Wh | 425 Wh | 7.8 h | 4.8 nights | 4.7 h | 15.2 h |
| 1,000 Wh | 850 Wh | 15.7 h | 9.7 nights | 9.4 h | 30.4 h |
| 2,000 Wh | 1,700 Wh | 31.4 h | 19.3 nights | 18.7 h | 2.5 days |
| 3,000 Wh | 2,550 Wh | 47.1 h | 29 nights | 28.1 h | 3.8 days |
| 5,000 Wh | 4,250 Wh | 3.3 days | 48.3 nights | 46.8 h | 6.3 days |
The CPAP column counts 8 hour nights at 11 W, a machine without its heated humidifier; with the humidifier the draw is about 56 W. The CPAP setup lists the stations that last two nights.
Why your hours can differ
The 85% is an assumption, adjustable in the calculator from 75% to 95%. On the 2,000 Wh example the essentials last 16.5 h at 75% and 20.9 h at 95%. The rated capacity guide explains where the rest of the energy goes.
The appliance figures are typical values for each class. An older refrigerator uses about 1.78 kWh a day in the data against 1.3 kWh for a modern one, which cuts the hours in the table by about a quarter or more. Read the label, or measure a day with a plug in meter, and enter the figure for an exact answer.
What drains the battery
Heat drains a battery fastest. A space heater on high draws 1,500 W and empties a 2,000 Wh station in about 1.1 h. Cooling is next: a 5,000 BTU window unit draws about 525 W while its compressor runs. In the essentials list the refrigerator takes 60% of the energy, and the router, which runs around the clock, most of the rest.
Making it last longer
- Switch off what you can. The router uses 224 Wh over an 8 hour night.
- Let the refrigerator coast. Food in a closed refrigerator stays cold for about four hours without power, so it can rest while the station runs something else.
- Recharge during the day. About 730 W of solar panels at 4 peak sun hours, counting 75% of the panel rating, put back a day of the essentials list; the solar guide explains the sums.
- Charge from the car. Each station page lists its car charging input, so a drive tops the battery up.
Planning for more than a day
Outages after storms can run for days. The 3 day outage, hurricane prep and winter storm furnace setups work out the longer cases against every station, and the 24 hour outage adds a TV, a laptop and the microwave to the essentials.
Check your own label
Watts vary by model and age. Check the label on your own appliance and enter it for an exact answer.