Before the Battery

Evidence page

Battery backup for a refrigerator

Short answer: plan on roughly 1,000–1,900 Wh per day at the outlet for a typical US refrigerator, then divide by about 0.72 to get the stored capacity you need. A 1,000 Wh station covers most of one day. A 2,000 Wh station covers one to two days. Beyond 48 hours, daily recharge decides the answer, not capacity.

Last updated 8 August 2026

The arithmetic, in full

Every figure below comes from your own EnergyGuide label, not from an assumed appliance profile. The example uses 500 kWh per year, a common mid-size US refrigerator.

  • 500 kWh/year ÷ 365 = 1,370 Wh per day at the outlet.
  • A 24-hour outage therefore needs 1,370 Wh delivered as AC.
  • Conversion losses: only about 85% of stored energy reaches an AC load. 1,370 ÷ 0.85 = 1,612 Wh.
  • Safety reserve: 15% of the pack is never planned against. 1,612 ÷ 0.85 = 1,896 Wh of stored capacity.

So a nominally “2,000 Wh” station is a one-day refrigerator machine, not a three-day one. Multiply the daily figure by three and the same arithmetic asks for roughly 5,700 Wh — a different class of hardware entirely.

The decision boundary

Past about 24 hours, the question stops being “how big” and becomes “does the cycle close”. Energy has to come back every day at least as fast as it is used. A 200 W solar panel in real winter conditions might return 400–600 Wh per day; a refrigerator asks for 1,370. That gap does not shrink by buying a larger battery — it is an architecture problem, and the honest answer is an installed system, a generator, or a shorter planning horizon.

Capacity is not compatibility

Watt-hours decide duration. Watts decide whether anything happens at all. A refrigerator compressor draws a steady running load and a much larger startup surge for a fraction of a second. A station can hold plenty of energy and still stall on that surge, which is why this publication treats startup as a separate pass/fail gate and refuses to derive running watts from kWh per day — an average energy rate is not a continuous output requirement.

What to measure

  1. The EnergyGuide kWh/year figure, or 24 hours on a plug-in power meter.
  2. Steady running watts while the compressor is running.
  3. The highest startup watts the meter records over a full day.
  4. What can realistically recharge, in Wh per day, during an outage.

Run it on your own numbers

Open the refrigerator outage check — it applies exactly the arithmetic above, shows every line of it, and abstains when the declared situation cannot be answered honestly. See also the methodology for where these factors come from.