To estimate how long a power station will last, multiply its capacity in watt-hours by 0.85, then divide by the average watts you'll draw. A 1,000 Wh station gives about 850 usable Wh: roughly 14 hours for a typical refrigerator averaging 60 W, or about 57 hours for a 15 W router.
Key facts
- Runtime (hours) ≈ capacity (Wh) × 0.85 ÷ average watts. It's an estimate; real losses vary by model and load.
- A fridge compressor cycles on and off. A typical fridge draws about 150 W while running but averages about 60 W over a day (about 1.45 kWh).
- A CPAP uses about 7–10 W with the humidifier off and about 22 W with it on (ResMed test data).
- A 1,500 W space heater empties a 1,000 Wh station in about half an hour.
- Solar recharge ≈ panel watts × peak sun hours, minus real-world losses.
How do you calculate power station runtime?
Use this formula:
Runtime (hours) ≈ capacity (Wh) × 0.85 ÷ average load (W)
The capacity is the watt-hour (Wh) rating on the spec sheet. If a battery lists amp-hours, multiply amp-hours by its voltage to get watt-hours. The watts, amps and Wh converter does this for you.
The load is what your devices draw on average, not the number on the power brick. Look up typical figures in our appliance wattage list, or skip the arithmetic with the power station runtime calculator.
Why multiply by 0.85?
You never get the full rated capacity out of an AC outlet, for two reasons.
- Inverter losses. Turning battery DC into 120 V AC costs some energy as heat. The inverter also draws a little power just to stay on, which matters most with tiny loads.
- Usable capacity. The battery management system keeps a reserve and cuts off before the cells are fully empty, to protect them.
Taking about 15% off for both is a reasonable planning number. Some models do better and some do worse, especially with very small or very large loads. Loads on the USB or 12 V DC ports skip the inverter, so they usually run a bit longer than the formula predicts.
How long will a power station run a refrigerator?
A fridge doesn't run all the time. The compressor turns on, cools, then shuts off, and the share of time it runs is the duty cycle. Our refrigerator data uses about 150 W while running and about a 40% duty cycle. That works out to about 1.45 kWh a day, or roughly 60 W on average.
ENERGY STAR listings for full-size models range from about 1.2 to 1.9 kWh a day, so the average falls between roughly 50 and 80 W. To get your fridge's average, take the yearly kWh on its EnergyGuide label, divide by 365, then divide by 24 and multiply by 1,000.
| Power station | Usable (× 0.85) | Typical fridge (≈60 W avg) | Range (50–80 W avg) |
|---|---|---|---|
| 500 Wh | 425 Wh | about 7 hours | 5–8.5 hours |
| 1,000 Wh | 850 Wh | about 14 hours | 11–17 hours |
| 2,000 Wh | 1,700 Wh | about 28 hours | 21–34 hours |
| 3,000 Wh | 2,550 Wh | about 42 hours | 32–51 hours |
Capacity is only half the test. The station also needs a surge rating high enough to start the compressor. Generator makers' charts list about 2,200 W for a fridge start, though newer inverter-compressor fridges usually surge much less. If the surge is too high, the station shuts off the moment the compressor kicks on. A chest freezer averages less than a fridge and lasts longer on the same battery.
Worked examples
CPAP on a 500 Wh station
425 usable Wh ÷ 22 W (humidifier on) ≈ 19 hours, a little over two 8-hour nights. With the humidifier off (about 10 W), it's roughly 42 hours, or five nights. See the CPAP backup guide for more detail.
Router and modem on a 300 Wh station
255 usable Wh ÷ 15 W ≈ 17 hours of home internet, as long as your provider's equipment in the neighborhood still has power.
Starlink on a 1,000 Wh station
Starlink lists the Standard kit at 75–100 W on average. 850 Wh ÷ 90 W ≈ 9.5 hours. The Mini, at 25–40 W, lasts roughly 21–34 hours.
A small outage kit on a 2,000 Wh station
A fridge (60 W average) + router (15 W) + two LED bulbs (18 W) comes to about 93 W. 1,700 Wh ÷ 93 W ≈ 18 hours.
Space heater on a 1,000 Wh station
850 Wh ÷ 1,500 W ≈ 0.57 hours, about 34 minutes. Resistive heat is the fastest way to drain a battery.
Runtime table for common devices
| Appliance | 500 Wh | 1,000 Wh | 2,000 Wh | 3,000 Wh |
|---|---|---|---|---|
| Refrigerator60 W average | 7.1 h | 14.2 h | 28.3 h | 42.5 h |
| Chest freezer24 W average | 17.7 h | 35.4 h | 70.8 h | 106.2 h |
| Mini fridge32 W average | 13.3 h | 26.6 h | 53.1 h | 79.7 h |
| CPAP machine22 W average | 19.3 h | 38.6 h | 77.3 h | 115.9 h |
| TV80 W average | 5.3 h | 10.6 h | 21.2 h | 31.9 h |
| Starlink90 W average | 4.7 h | 9.4 h | 18.9 h | 28.3 h |
| Wi-Fi router and modem15 W average | 28.3 h | 56.7 h | 113.3 h | 170 h |
| Window air conditioner396 W average | 1.1 h | 2.1 h | 4.3 h | 6.4 h |
| Portable fridge21 W average | 20.2 h | 40.5 h | 81 h | 121.4 h |
| Electric blanket50 W average | 8.5 h | 17 h | 34 h | 51 h |
Hours = capacity × 0.85 ÷ average watts. Fridges and freezers cycle, so their average is well below the running watts.
What about UPS runtime?
The same idea applies to a computer UPS: stored energy divided by load. Many UPS units use small batteries and publish their own runtime charts at different loads. Use the maker's chart when there is one, because losses and usable capacity vary more than with a power station. For hours of backup rather than minutes, a power station is the better fit.
How long does it take to recharge with solar?
Rough solar input per day is panel watts × peak sun hours. A peak sun hour is one hour of sunlight at full strength. Your daily total depends on location and season; NREL publishes solar resource maps for the US.
Say your site gets 4 peak sun hours. A 200 W panel's best case is about 800 Wh a day. Real harvest is lower: panels lose output when hot, tilted wrong, dirty or partly shaded, and charging has its own losses. Two more limits apply:
- Max solar input. Every station caps how many panel watts it can accept. Extra panels beyond that cap add little.
- Daily balance. If your loads use more per day than the panels put back, the battery still runs down, just more slowly. A fridge alone uses about 1.2–1.9 kWh a day.
Wall charging is much faster, and car charging is slow. Check the spec sheet for each input's wattage.
How does battery chemistry affect lifespan?
Most power stations use either LFP (lithium iron phosphate, LiFePO4) or NMC lithium-ion cells. One manufacturer's guide gives roughly 3,000–4,000+ charge cycles to 80% capacity for LFP, against about 500–1,000 for NMC.
As a battery ages, its capacity shrinks, so runtime shrinks with it. Plan with a little headroom, and check whether the cycle rating on the spec sheet is to 70% or to 80% of original capacity.
Still deciding between battery and fuel? Read power station vs generator, or plan an outage load list with what to run during a power outage.
Questions people ask
How long will a 1,000 Wh power station run a fridge?
Roughly 11–17 hours for a typical full-size fridge averaging 50–80 W, provided the station's surge rating can start the compressor.
Why does my power station die sooner than the math says?
Inverter losses, battery reserve, cold temperatures and an aging battery all cut runtime. Devices with heaters or compressors also draw more than their average at times.
How do I convert amp-hours to watt-hours?
Multiply amp-hours by the battery voltage. For example, 100 Ah at 12.8 V is 1,280 Wh.
Can solar panels keep a power station charged during an outage?
For small loads like phones, lights, a router or a CPAP, often yes. For a fridge you'd need enough panel watts and sun to replace about 1.2–1.9 kWh a day, which a single small panel can't do.
Does a power station lose charge in storage?
Yes, slowly. Follow the storage advice in its manual and top it up before storm season so it's full when an outage hits.
Sources
- ENERGY STAR: Refrigerators
- ResMed: Power consumption of Air10 devices (PDF)
- Starlink: Standard kit specification sheet (PDF)
- Starlink: Mini kit specification sheet (PDF)
- Champion Power Equipment: Generator wattage chart (PDF)
- Anker SOLIX: LiFePO4 vs lithium-ion portable power stations
- NREL: Solar resource maps and data
