Battery backup for a refrigerator: how long a power station keeps food cold, from the EnergyGuide number

A refrigerator is the appliance most people actually lose money on in an outage, and the one most brand calculators get wrong, because they multiply the compressor’s running watts by 24 hours and quote a battery three times bigger than you need. The honest number is on the yellow label. An average full-size refrigerator draws about 50 to 75 W averaged over a day, so a 1 kWh power station keeps one cold for most of a day and a 2 kWh unit for most of two.

The number on the label, not the nameplate

The EnergyGuide label states kilowatt-hours per year, measured with the door closed in a 90 degree room. Divide by 8,760 hours and you have the average draw, compressor cycling included. ENERGY STAR lists the Frigidaire FFHI1835V, an 18.3 cu ft top-freezer, at 453 kWh per year: 52 W. Whirlpool’s 30.5 cu ft WRFF3336S is listed at 645 kWh per year: 74 W. The refrigerator wattage guide has the method and more models. The table above runs on the smaller fridge; scale by your own label.

Why the small number needs a big inverter

The compressor starts several times an hour, and each start draws locked-rotor current for a fraction of a second, typically five to seven times its running current. That spike is not on the label. Every pick here carries at least 1,800 W continuous and 3,000 W surge, which is more headroom than any residential compressor needs, and it is the reason a 300 Wh camping unit with a 300 W inverter is not on this list even though its watt-hours would run the fridge for four hours. The mechanism is in running watts versus surge watts.

Set it up before the storm

Four of the five picks have a UPS mode, explained in the pass-through guide: plug the unit into the wall and the fridge into the unit, and when the grid drops the battery takes over in 10 to 20 milliseconds. The fridge never notices, you do not have to be home, and the battery is full when the outage starts rather than whatever it drained to on the shelf. That is worth more than an extra 200 Wh of capacity, which is why the DELTA 3 leads a list that contains larger units. The winter storm plan puts the refrigerator in order with the other loads.

What the runtime buys you

USDA’s rule is that a closed refrigerator keeps food safe for about 4 hours without power and a full freezer for about 48. A 1 kWh unit turns the refrigerator’s 4 hours into roughly 16; a 2 kWh unit turns it into a day and a half. The 1 kWh roundup ranks the smaller class on its own. A chest freezer wants the same class of inverter for a fraction of the energy; the chest freezer wattage guide has those figures. Keep the door closed anyway, and put a thermometer inside: the battery buys time, and the thermometer tells you whether the time was enough. The reason a 1,024 Wh sticker becomes about 870 Wh in the table is in usable capacity versus advertised, and the sump pump page is the same arithmetic on a much hungrier motor.