How long will a battery run a refrigerator?

Average watts decide runtime — not the watts on the label

A refrigerator's rating is the draw while the compressor runs. Over a day the compressor cycles, so the backup calculator models a fridge as rated watts × run-hours per day: its default 150 W refrigerator runs 8 hours in 24, which is 1.2 kWh a day and a 50 W average. Runtime for any battery is then just usable watt-hours ÷ average watts.

That is also how the calculator sizes in the other direction: backup hours × average watts = watt-hours needed. Its default critical set — the fridge, a 200 W chest freezer running 10 hours a day, and 15 W of temperature monitoring that never sleeps — averages 148 W and uses 3.56 kWh a day, so 48 hours of cover needs 7.12 kWh. A runtime question and a sizing question are the same equation read from opposite ends.

Runtime table, from the calculator's defaults

Read your battery off the row. The left column is the calculator's default refrigerator alone; the right adds its chest freezer and the monitoring gear, which is the set most people actually want to protect:

• The table counts the battery's full capacity as usable, the same way the calculator's backup-needs figure counts raw energy. If your plan only draws a battery down partway, scale the runtime by the same share: half the usable energy, half the hours.
• The calculator's full default list — a second fridge and an upright freezer included — uses 6.32 kWh a day. Shedding the non-critical half of the list during an outage is the cheapest runtime you can buy.

The food-safety clock runs even when the battery doesn't

Runtime is not the only deadline. The calculator carries the food-safety hold times alongside its power math: an unopened refrigerator keeps food safe about 4 hours, a half-full freezer about 24 hours, and a full freezer about 48 hours. Its risk scale turns on the same numbers — under 24 hours of backup rates high risk, 48 hours or more rates low.

That reframes the battery question. You do not need to run the fridge forever; you need to bridge to power restoration or to the next recharge. A 2 kWh battery that runs the fridge alone for about 40 hours pairs naturally with the freezer's own 48-hour hold: the freezer coasts unopened while the battery carries the fridge, and together they cover the window the calculator calls low-risk.

Stretching the hours you have

Three levers, all inside the same equation:

• Cut the average. Dropping the fridge's average draw from 50 W to 40 W — a newer, smaller, or better-sealed unit — stretches a 5 kWh battery from 100 to 125 hours. The refrigerator energy cost calculator shows what a replacement draws over a year; the same watts decide outage runtime.
• Keep the doors shut. The hold times above assume unopened doors; the freezer's 48 hours is a coasting budget, not a target to spend on browsing.
• Recharge mid-outage. Runtime only has to bridge to the next solar day or generator run, which is why this load list is step one of whole-home backup planning rather than a standalone purchase.