How we calculate power station runtime and size

The formula

Hours a station runs one appliance

rated Wh × 0.82 ÷ (appliance W + inverter W)

Inverter W is 10 W for stations under 1,000 Wh, 15 W from 1,000 to 1,499 Wh, and 18 W from 1,500 Wh up. It applies only to appliances plugged into the AC outlets. USB and 12 V loads skip the inverter.

The 82% and the inverter figures come from the runtime calculator on Jackery's US product pages. The calculator's code (getRunningTime in Jackery's site script) divides capacity times 0.82 by the load's watts plus a self-draw that Jackery sets for each model: 10 W on the Explorer 300, 15 W on the Explorer 1000 v2, and 18 W on the Explorer 1500 v2 and 2000 v2. These are in the page code rather than a published specification.

No other maker we cover publishes a figure for usable capacity or inverter draw, so we apply Jackery's numbers to every station by size and say so wherever a runtime appears. A maker's own calculator may give a different answer for its own station.

Rated capacity is measured at the battery. Some of that energy is lost turning the battery's direct current into 120 V household power, and an inverter that is switched on draws power even when little is plugged in. That is why the formula takes a share of the rated figure and adds a fixed draw for AC loads.

Sizing a list of appliances

The sizing tool adds up watt-hours for a day: each appliance's watts times the hours you enter, plus battery watt-hours times charges for phones, laptops and e-bikes. It adds the inverter's draw for as many hours as anything runs on AC, then divides by 0.82 to give the rated capacity a station needs.

It also checks power, not only energy. Every appliance running at the same time has to fit under the station's continuous AC output, and the biggest motor or compressor's start-up draw has to fit under the station's peak rating. A station that has enough watt-hours but too little output is marked as too small.

Worked examples

A CPAP on a 1,024 Wh station. ResMed lists the AirSense 11 at 56.1 W typical. On AC: 1,024 × 0.82 ÷ (56.1 + 15) = 11.8 hours, a little over 1 nights of 8 hours.

A refrigerator on a 2,048 Wh station. A fridge's compressor switches on and off, so the useful figure is the day's average. The Whirlpool WRT541SZD, a 21.3 cu ft top-freezer fridge, is listed at 399 kWh a year on ENERGY STAR, which is 399 × 1,000 ÷ 8,760 hours = 45.5 W on average. 2,048 × 0.82 ÷ (45.5 + 18) = 26.4 hours.

Where appliance figures come from

Each appliance in the tool names the model its figure comes from and links the source: the maker's spec sheet or manual, the EnergyGuide label, or the ENERGY STAR product finder. For appliances that cycle on and off (refrigerators, freezers, dehumidifiers) we use the average from the label's yearly kilowatt-hours. For start-up draw we use only a figure the maker publishes; when there is none, the tool cannot check start-up for that appliance and the page says so.

The hours a day in each preset are our assumptions, there to give a starting point. Change them to match how you use things.

What the numbers leave out

Your appliance is not the model we used. Check its label or manual and type its watts into the tool if they differ.
Cold weather, heat and battery age all reduce what a station delivers. Makers rate cycle life to a share of original capacity (often 80%), which the model pages list.
Running near a station's full output can trigger its protection before the battery is empty.
Charging the station while it runs (pass-through, solar) extends runtime. The tool assumes no charging during the day.

Prices

Store prices come from each brand's public US store data; Amazon prices come from Amazon's Product Advertising data for our Associates account. Both are fetched when the site is built, twice a day, and every price shows the date it was checked. We ignore members-only and app-only prices, and bundles with panels or extra batteries. Price history on model pages is built from these twice-daily readings.