Battery size is Wh. Output is W. Mixing them up is how people buy the wrong station. Here is the difference, and a calculator that checks both at once.
Every power station lists two big numbers. One ends in Wh, the other in W. They look alike, but they answer two different questions.
Two questions, two numbers
Can it power this at all? That is the W Watts. Power right now. The station has a maximum it can put out; each appliance has a draw. number. Watts are power right now. The station has a maximum it can put out, and every appliance has a draw. If the draw is higher than the station's output, the appliance will not run, however full the battery is.
For how long? That is the Wh Watt-hours. Battery size. How much energy is stored. 1,000 Wh runs a 100W device for about 8.5 hours after losses. number. Watt-hours are the size of the battery: how much energy is stored inside. More Wh means more hours at the same draw.
Think of a water tank. Wh is how much water is in the tank. W is how fast it can flow out of the tap. A big tank with a thin pipe cannot fill a bath quickly. A wide pipe on a small tank empties it fast.
watt-hours = watts x hours
100 W for 2 hours = 200 Wh
hours = Wh x 0.85 / W
1,024 Wh x 0.85 / 100 W = 8.7 hours
The 0.85 is there because the station loses some energy turning battery power into wall power. We take off about 15% everywhere on this site.
Two ways to buy the wrong station
Too few watts. The EcoFlow RIVER 3 Plus has a 286 Wh battery and puts out up to 600 W. A typical microwave draws about 1,000 W while it runs. The battery holds enough energy for about 15 minutes of that, but the output is too low, so the microwave will not run at all.
Too few watt-hours. The EcoFlow DELTA 3 Plus puts out up to 1,800 W, so it can run a 1,500 W space heater. But its 1,024 Wh battery keeps that heater going for only about 35 minutes.
So check both, in this order. First W: is the station's output higher than the appliance's draw? Then Wh: is the battery big enough for the hours you need?
Calculator
Can it run it, and for how long?
Appliance
Output check (W)Yes, it runsSpace heater draws about 1,500 W. The DELTA 3 Plus puts out up to 1,800 W.
Runtime (Wh)35 minutes1,024 Wh x 0.85 / 1,500 W
Appliance watts are typical values, not measurements of your device. Check the label on yours. Runtime assumes 85% of the battery is usable.
One more number: surge
Some appliances pull much more power for a moment when a motor starts, like a fridge compressor or a pump. Stations list a Surge A short burst of extra output the station can deliver for a second or two, for motors starting. rating for that moment. The DELTA 3 Plus, for example, is rated for 1,800 W continuously and lists 3,600 W of surge. If an appliance trips the station the instant it starts, its start-up draw may be higher than the station's surge rating.
kW and kWh
Bigger units work the same way. 1 kW is 1,000 W. 1 kWh is 1,000 Wh. Your electricity bill counts kWh, so the EcoFlow DELTA Pro 3's 4,096 Wh battery holds about 4.1 kWh, the same unit your utility charges for.
Rules of thumb
Add up the watts of everything you will run at the same time. That total must stay under the station's output.
For battery size, multiply each appliance's watts by its hours, add them up, and divide by 0.85.
