How to Calculate Power Station Runtime

The two numbers on a power station listing

Every portable power station listing on this site shows a capacity figure and a continuous output figure. The capacity is given in watt-hours (Wh) or kilowatt-hours (kWh). The continuous output is given in watts (W) or kilowatts (kW). These are two separate measurements, and you need both to understand what a station can do.

The capacity tells you how much energy the station can store, like the size of a reservoir. The output tells you how fast that energy can be supplied, like the width of a pipe. A large capacity with a small output can power low-draw devices for a long time; a small capacity with a large output can power demanding devices briefly.

You can read more about how to read a listing in how to read a power station spec sheet.

Watt-hours: the stored energy

A watt-hour is a unit of energy. It combines the power draw of a device with the time it runs. A device that draws one watt for one hour uses one watt-hour of energy. The capacity number on a listing is the total energy the station can deliver before it needs recharging.

The U.S. Energy Information Administration explains that electricity is measured in units of power called watts, and that a kilowatt is 1,000 watts. A kilowatt-hour is 1,000 watt-hours. When a listing says a station has a certain capacity, that is the stored energy, not the maximum rate.

If you are comparing capacity across stations, see watt-hours vs amp-hours for the difference between those units.

Watts: the delivery rate

Watts measure the rate at which electricity is used. The continuous output figure on a listing is the maximum power the station can supply to its AC outlets without interruption. Some listings also show a surge or peak figure, which is a temporary boost for starting motors or compressors.

The output figure is separate from capacity. You can compare stations with similar capacity but different output, and the output determines what devices the station can start and sustain. For more on surge, see surge power vs constant.

The simple relationship between capacity, power, and time

To estimate how long a station will run a particular device, divide the capacity in watt-hours by the average power draw of the device in watts. The result is a rough time in hours. This is a straightforward relationship, but it only works if you have accurate numbers for both sides.

The capacity is printed on the listing. The average power draw of your device is usually on a label on the device or in its manual. The maker's product page may also list the continuous output and any surge rating for the station.

This site does not publish runtime figures for specific stations because the catalogue does not include device-specific draw data, efficiency figures, or idle consumption. A runtime figure on a listing is not a statement from this site; it is the seller's or maker's claim, and you should read it on the listing and on the maker's page.

Why a precise runtime is hard to state

Even with the formula in hand, actual runtime can differ from the estimate. The station's inverter converts DC to AC with some energy loss, the station draws a small amount of power even when idle, and many devices do not run at their rated wattage continuously. Motors and compressors draw a surge at startup, then settle to a lower draw.

The maker's documentation is the authority for how the station behaves. Some makers, such as Anker SOLIX, provide a backup time calculator on their website. These tools are based on the maker's own assumptions and should be treated as an estimate, not a guarantee. Always read the notes that accompany any runtime figure.

Comparing by capacity tier

Because runtime depends on so many variables, this site recommends comparing stations by their stated capacity bands. The buying guides group stations into capacity tiers, such as 1,000Wh, 2,000Wh, and 5,000Wh. Within a tier, you can compare the continuous output, the battery chemistry, and whether a solar panel is included. This approach lets you focus on the features that matter most for your use case.

Think about the job you want the station to do. For a weekend campsite, a smaller capacity may be enough; see best portable power station for camping. For a home office desk with a UPS requirement, look for a station that lists UPS mode; see best portable power station with UPS. For storm season at home, a larger station with room for expansion may fit; see best portable power station for home backup.

What to pick for your situation

Questions

How do I estimate runtime myself?

Divide the station's watt-hour capacity by the average power draw of the connected device in watts. That gives a rough time in hours. The device's wattage is usually on a label or in its manual. This site does not provide runtime figures because it does not have the device-specific data.

Why does this site not list runtime for each station?

The catalogue that this site is built from includes only the stated capacity, output, chemistry, and a few other details. It does not include runtime measurements, efficiency figures, or idle consumption. Listing a runtime would be an assumption rather than a stated detail.

What is a watt-hour?

A watt-hour is a unit of energy equal to the energy used by a device that draws one watt for one hour. It is the product of power in watts and time in hours.

What is a watt?

A watt is a unit of power, or the rate at which electricity is used. The U.S. Energy Information Administration describes electricity as measured in watts.

Should I use continuous output or surge for my calculation?

Use the device's steady-state power draw for the estimate. Surge is the initial boost that motors and compressors need for a short moment. The station's continuous output tells you whether it can sustain the device over time; the surge figure tells you whether it can start it.