How the estimates are calculated

Every runtime on this site is arithmetic on published numbers. We do not test hardware, so nothing here is a measurement. This page explains the formula, the checks and the limits, so you can redo any number yourself.

The runtime formula

Runtime (hours) = battery Wh x inverter efficiency / load W

• Battery Wh is the capacity the maker publishes for the base unit, without add-on batteries.
• Inverter efficiency is the share of battery energy that reaches the AC outlets. Some is lost turning the battery's DC into household AC, and the inverter draws a little power just by being on. When a maker publishes an efficiency figure we use it. Most do not, so we use 0.85 and mark it as an assumption on the page.
• Load W is the appliance's running watts. Sources often disagree, so we keep every sourced figure and show the range: the runtime at the highest figure first, then at the lowest.

Example: a 1,024 Wh station running a 100 W load gives 1,024 x 0.85 / 100, about 8.7 hours.

Fridges and freezers: average draw

A fridge's compressor cycles on and off, so its running watts overstate what it uses over a day. For fridges and freezers we also work out an average draw from ENERGY STAR certified-model data: the median annual energy use (kWh a year) divided by 8,760 hours in a year. That average is what the 24-hour outage pages use. The running and starting watts still decide whether the station can run it at all.

The two limits

1. Rated output. The appliance's running watts must fit under the station's rated (continuous) AC output. If they don't, the station shuts off or refuses the load, however big the battery. When the sourced range straddles the rating we mark it "Check": it depends on your model.
2. Starting surge. Motors and compressors (fridges, freezers, pumps, air conditioners) draw several times their running watts for a moment when they start. That starting figure must fit under the station's published surge rating. Some charts list only the extra watts on top of running watts (Generac calls them additional starting watts); we add the two to get the total peak. If the maker doesn't publish a surge rating, we say so and mark it "Check" rather than guess. Heaters, kettles and other heating loads have no motor start.

Several appliances at once

Running watts add up. For the starting peak we assume one motor starts at a time while everything else runs: total running watts plus the largest single jump from running to starting watts. If two motors start together the peak is higher.

What the estimates leave out

• Batteries hold less as they age and in the cold, and most stations keep a little in reserve.
• Real appliances differ from the published figures. The label on yours, or a plug-in watt meter, beats any table.
• Boost modes (EcoFlow X-Boost, Anker SurgePad, BLUETTI Power Lifting) let heating loads run above the rated output at reduced power. We list them but don't count them.
• Solar recharge times assume the station's full rated solar input, which panels rarely deliver all day.

Where the numbers come from

Station specs come from each maker's own US product or spec page, read on the date shown in each page's sources. Appliance watts come from public sources: ENERGY STAR data, U.S. Department of Energy guidance, generator makers' wattage charts and appliance spec sheets. A field with no source stays empty and the page says "Not published". If you find a better source for any number, tell us and we will update it.