The best cheap portable power stations of 2025: Expert tested and reviewed

Manufacturers typically offer different runtimes for things like lamps, refrigerators, CPAP machines and so on, but if you want to work this out for yourself you can need two figures. 

First, you need the power rating of the device you plan on running, which can usually be found on a label on the device, and is measured in Watts (W). You also need to know the capacity of the power station, measured in Watt hours (Wh), which should be printed somewhere on the device. 

Let’s say you have a device that consumes 300W and a power station that has a capacity of 768Wh, you can get a ballpark runtime for the device using the following equation:

(768 x 0.85)/300 = 2.2 hours

Note that the capacity of the power station is multiplied by 0.85 to account for efficiency losses.