Refrigerator battery calculator

Estimate how long a published battery capacity covers your refrigerator’s average draw, and the watt-hours a duration needs. Watts are a rate. Watt-hours are an amount. A battery can have enough watt-hours and still fail to start the compressor.

Worked example, before you enter your own numbers

A refrigerator that uses 500 kWh per year averages 57.0776 W. The 10 W idle allowance is added first, so the AC-equivalent load is 67.0776 W. For a 2,048 Wh battery, the exact runtime is 23.3568 hours. Rounded to one decimal, that is about 23.4 hours. The minimum capacity for 24 hours is 2,104.4 Wh. That is 56.4 Wh more than 2,048 Wh, so this capacity does not cover the full 24-hour plan.

The equations are average watts = annual kWh × 1000 / 8760, AC-equivalent watts = average watts + idle watts, runtime = capacity × efficiency × (1 − reserve) / AC-equivalent watts, and minimum capacity = duration × AC-equivalent watts / (efficiency × (1 − reserve)). With the defaults that is runtime = capacity × 0.85 × 0.90 / (average watts + 10). JavaScript is not required to read this example.

Worked example for 500 kWh per year and 24 hours, four published batteries in suitability order.
Model	Capacity	Continuous	Published surge	Planning result	Source check	Link
EcoFlow DELTA 3 Plus	1,024 Wh	1,800 W	3,600 W	Shortfall: 1,080.4 Wh below the planning minimum. Planning runtime 11.7 hours.	Spec block matched 1,024 Wh, 1,800 W total, and 3,600 W surge. The same page also describes an X-Boost figure of 2,200 W, which is not the continuous rating used here. Capacity: The specifications block included “1024 Wh.”	Manufacturer information (opens in a new tab)
Jackery Explorer 1000 v2	1,070 Wh	1,500 W	3,000 W	Shortfall: 1,034.4 Wh below the planning minimum. Planning runtime 12.2 hours.	A specifications row matched 1,070 Wh, 1,500 W rated, and 3,000 W surge. A description sentence on the same page says 1,024 Wh. This site did not replace 1,070 Wh. Capacity: The page included “30.4Ah/35.2V DC (1070 Wh)” and data-capacity 1070. The product description also says “Delivers 1024Wh Capacity and 1500W Output.”	Manufacturer information (opens in a new tab)
Jackery Explorer 2000 v2	2,042 Wh	2,200 W	4,400 W	Shortfall: 62.4 Wh below the planning minimum. Planning runtime 23.3 hours.	Official text matched 2,042 Wh, 2,200 W continuous, and 4,400 W surge. The manufacturer’s refrigerator wording on that page is not a test by this site. Capacity: The page title included 2042Wh, and the description included 2042Wh of capacity.	Manufacturer information (opens in a new tab)
EcoFlow DELTA 3 Max	2,048 Wh	2,400 W	4,800 W	Shortfall: 56.4 Wh below the planning minimum. Planning runtime 23.4 hours.	Official text matched 2,048 Wh, 2,400 W output, and 4,800 W surge. An X-Boost mention of appliances up to 3,400 W is not used as the continuous or surge rating. Capacity: The meta description included 2048Wh capacity.	Manufacturer information (opens in a new tab)

Your refrigerator

How do you know the energy use? Annual kilowatt-hours, such as the EnergyGuide figure Measured average watts Running watts and a compressor duty cycle

Annual energy use (kWh/year)

Greater than 0 and at most 20,000. This is not continuous running watts.

How long do you want to plan for? 8 hours 12 hours 24 hours 36 hours 48 hours Custom

Known startup watts, if you have them

Leave this blank if you do not know. Startup compatibility stays unconfirmed, and surge ratings are not compared.

Preferred published battery or your own capacity

Planning assumptions (efficiency 0.85, reserve 10 percent, idle 10 W)

Inverter efficiency

0.85 means 85 percent. Must be greater than 0 and at most 1.

Reserve percent

10 means keep 10 percent unused (a reserve fraction of 0.10). It must be under 100.

Idle allowance (AC-equivalent watts)

Added to average watts before efficiency. Default 10 W. It is not a second, hidden loss.

Enter the energy use and choose Calculate. The math stays in this browser. The worked example above remains available if JavaScript is off.

What the inputs mean

Annual kilowatt-hours become average watts by multiplying by 1,000 and dividing by 8,760, the hours in a non-leap year. A measured average is used as-is. Running watts times a duty-cycle fraction is another average. All three describe energy over time, not the brief startup spike.

Continuous watts on a power station are the output it is published to hold. Surge watts are a short published peak. Compare those ratings only to a startup figure you actually know. If you do not know it, this page will not pretend the comparison happened.

Efficiency, reserve, idle, age, and temperature move the real result. A cold garage, an old battery, or a refrigerator that runs more because the kitchen is hot can use the reserve you set aside. The defaults are planning choices: efficiency 0.85, reserve 0.10, and a 10 W idle allowance added to average watts before that efficiency is applied.

Read the full method, the watts explainer, and the EnergyGuide page before treating a result as a shopping decision.

Common questions

Does matching the watt-hours mean my refrigerator will run?

No. The result is an energy estimate under the assumptions you leave in the form. It does not confirm the compressor will start, and it does not measure food temperature.

What if I do not know startup watts?

Leave the field blank. Startup compatibility is not confirmed, and the published surge figures are not compared. You still get the energy estimate.

Where does the 10 W idle go in the formula?

It is an AC-equivalent allowance added to average watts before inverter efficiency. Runtime is capacity × 0.85 × 0.90 ÷ (average watts + 10). There is no second, hidden derating.