Power Station Runtime Calculator

Power station or enter capacity below

Battery capacity (Wh)

Appliance preset

Average load (W)

Output used

Keep in reserve %

Estimated runtime

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Usable energy

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Box-label runtime

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Tip: fridges and freezers cycle on and off, so their average draw is roughly a third of their running watts. The presets already account for that.

New to this? The four terms you need

Watts (W): How much power something uses at a given moment. It decides whether a power station or generator can run it at all.
Watt-hours (Wh): Power over time: watts × hours. It's the size of a battery, and decides how long things keep running.
Surge (starting watts): The short burst of extra power a motor needs to start, like a fridge, pump or AC. It lasts a split second but has to be covered.
LiFePO4: The battery type used in most new power stations. It lasts thousands of charge cycles and is the safer choice indoors.

The runtime formula

Runtime (hours) = Capacity (Wh) × efficiency × (1 − reserve) ÷ Load (W)

For example, a 1,024 Wh power station running a 60 W average load from its AC outlet: 1,024 × 0.85 ÷ 60 ≈ 14.5 hours. The box-label math (1,024 ÷ 60 = 17 hours) overstates it by about 15%.

Typical runtimes on a 1,000 Wh power station

Appliance	Average draw	Approx. runtime
Wi-Fi router + modem	20 W	~42 hours
CPAP (no humidifier)	40 W	~21 hours (2–3 nights)
Refrigerator (average incl. cycling)	60 W	~14 hours
Box fan	60 W	~14 hours
50" LED TV	100 W	~8.5 hours
Window AC (8,000 BTU)	700 W	~1.2 hours
Space heater (high)	1,500 W	~35 minutes

Heating and cooling appliances drain batteries fastest. If you need to run them for hours, look at expandable systems or a generator. Use the power station size calculator to size a full appliance list.

How to find your appliance's watts

Check the label or nameplate on the back or bottom. If it only lists amps, multiply amps × 120 V.
Most power stations show live input and output watts on their screen. Plug the appliance in for a few minutes and read it.
An inexpensive plug-in watt meter will measure average consumption over a full day, which is the most accurate way to measure a fridge.

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Power stations that fit this use

Specs come from the manufacturers. Prices change often, so check the current price before you buy. Want every model side by side? See the comparison chart.

EcoFlow RIVER 2

Phones, laptops, CPAP for one night, camping

256 Whcapacity
300 Woutput
110 Wsolar input
7.7 lbweight

Check price

EcoFlow DELTA 2

Fridge + router + lights during a 1-day outage

1,024 Whcapacity
1,800 Woutput
500 Wsolar input
27 lbweight

Check price

BLUETTI AC180

Most capacity in the 1 kWh class

1,152 Whcapacity
1,800 Woutput
500 Wsolar input
35.2 lbweight

Check price

Frequently asked questions

How long will a 1,000 Wh power station run a refrigerator?

A typical refrigerator averages about 60 W over a day (its compressor cycles on and off). After roughly 15% conversion losses, a 1,000 Wh unit delivers about 850 Wh of usable energy, or around 14 hours. Older or larger fridges can cut that in half.

How long will a power station run a CPAP?

A CPAP without a humidifier draws roughly 30–60 W. A 500 Wh power station will usually last about two nights, and longer on DC power with a 12 V adapter. Heated humidifiers can triple consumption.

Why is real runtime shorter than capacity divided by watts?

Converting the battery's DC power to 120 V AC wastes 10–15% as heat, the inverter itself draws a few watts at idle, and cold temperatures reduce usable capacity. Our calculator applies these losses so the estimate matches real use.

Is it better to use DC or AC outputs?

Use DC (USB-C, USB-A or 12 V car port) whenever your device supports it. DC skips the inverter, so you lose only about 5% instead of 10–15%, and you avoid the inverter's idle draw.

Related guides

How-To

Can a Power Station Run a Space Heater? (Why It's Usually a Bad Idea)

A 1,500 W space heater drains a 1,000 Wh power station in about 35 minutes. The math, and better ways to stay warm when the power is out.

October 20, 2026, 2 min read

Buying Guides

Best Power Station for CPAP: How to Choose (and How Many Nights You'll Get)

How to pick a power station for your CPAP machine: how many watt-hours you need, why DC power doubles runtime, and which battery sizes cover 1, 2 or 3 nights.

October 20, 2026, 3 min read

How-To

Can a Power Station Run a Window Air Conditioner? (And for How Long?)

Yes, a 1,800 W+ power station can run a small window AC, but only for 1–4 hours on a 1–2 kWh battery. The math, and how to stretch runtime in a summer outage.

October 20, 2026, 3 min read