How accurate is this calculator?

It is an estimate, not a measured result. We use the battery’s rated watt-hours times 0.85 (inverter and battery losses), divided by your devices’ average draw. Cold weather, an old battery and devices that work harder than their label (a fridge on a hot day) all shorten runtime.

What is the difference between running watts and start-up watts?

Running watts is what a device draws while it works. Start-up (surge) watts is the short spike when a motor or compressor kicks on. A fridge might run at 150 W but spike to 1,000 W for a second. A power station has to handle both: the surge rating for the spike, the continuous rating for the rest.

Why does the fridge show more hours than the math suggests?

Fridges, freezers, space heaters and AC units cycle on and off. A fridge compressor runs about a third of the time, so its average draw is about a third of its running watts. The calculator uses each device’s typical duty cycle. You can see it under the device name.

Can I use this for a generator or solar setup?

The surge and continuous checks apply to any inverter. The runtime number only makes sense for a battery. Pick “Enter my own numbers” and type the battery capacity in watt-hours.

What about medical devices like a CPAP or oxygen concentrator?

The calculator will give you a runtime, and our CPAP page explains how to stretch it (turn off the heated humidifier, use the 12V/DC cable). Still, never depend on one battery for life-support equipment. Have a second unit or another plan.

Will it run my…? Free tool

Portable power station calculator

Add the things you need to keep running, pick a power station, and get a plain answer: how many hours, and whether it can handle the start-up surge.

Step 1

What do you want to run?

CPAP (no humidifier)
Number of CPAP (no humidifier): 1

Add more

Step 2

Pick a power station

1,800 W output · 3,600 W surge · full specs

For a CPAP (no humidifier) on the EcoFlow DELTA 3 Plus:

Yes, it can run this

Estimated runtime

5 days

About 15 nights at 8 hours a night.

Running load: 7 W
Average draw: 7 W
Biggest surge: 10 W

• Everything fits within the 1,800 W output and 3,600 W surge rating.

Math: battery Wh × 0.85 ÷ average watts. Cold weather, battery age and screen-on time all shorten this.

Power stations that can run this

EcoFlow RIVER 3 Plus
about 35 hrs (4 nights) · $180–$300
Check price
BLUETTI Elite 30 V2
about 35 hrs (4 nights) · $180–$280
Check price
Jackery Explorer 300 v2
about 35 hrs (4 nights) · $200–$280
Check price

We may earn a commission if you buy through these links. It doesn't change your price. How we make money

Price ranges checked by hand on October 9, 2026. Prices change often.

About 5 days

15 nights · 1 device on EcoFlow DELTA 3 Plus

See result

How the math works

Every power station has two numbers that matter. Watt-hours (Wh) is the size of the tank: how much energy is stored. Watts (W) is the size of the pipe: how much power can flow out at once.

Runtime in hours = battery Wh × 0.85 ÷ the average watts of everything plugged in. The 0.85 covers the energy lost turning battery power into wall power. For devices that cycle on and off, like a fridge, we use their average draw rather than the running number on the label.

Before the runtime matters, the unit has to be able to start your devices at all. We check two things: the total running watts against the continuous output, and the biggest start-up spike (with everything else already running) against the surge rating. If either fails, the answer is no, however big the battery is.

Where the device numbers come from

The defaults come from manufacturer spec sheets, Energy Star data and utility company wattage charts. They are typical values for a common current model. If you know your own device’s label wattage, type it in; the label number is usually the maximum, so real draw is often lower.

Common questions

How accurate is this calculator?: It is an estimate, not a measured result. We use the battery’s rated watt-hours times 0.85 (inverter and battery losses), divided by your devices’ average draw. Cold weather, an old battery and devices that work harder than their label (a fridge on a hot day) all shorten runtime.
What is the difference between running watts and start-up watts?: Running watts is what a device draws while it works. Start-up (surge) watts is the short spike when a motor or compressor kicks on. A fridge might run at 150 W but spike to 1,000 W for a second. A power station has to handle both: the surge rating for the spike, the continuous rating for the rest.
Why does the fridge show more hours than the math suggests?: Fridges, freezers, space heaters and AC units cycle on and off. A fridge compressor runs about a third of the time, so its average draw is about a third of its running watts. The calculator uses each device’s typical duty cycle. You can see it under the device name.
Can I use this for a generator or solar setup?: The surge and continuous checks apply to any inverter. The runtime number only makes sense for a battery. Pick “Enter my own numbers” and type the battery capacity in watt-hours.
What about medical devices like a CPAP or oxygen concentrator?: The calculator will give you a runtime, and our CPAP page explains how to stretch it (turn off the heated humidifier, use the 12V/DC cable). Still, never depend on one battery for life-support equipment. Have a second unit or another plan.