Size your backup power for the biggest STARTING number, not the sum of running watts — that one rule prevents the most common backup-power failure there is: a battery that covers everything on paper and still shuts down the moment the refrigerator tries to start.
Two numbers, not one
Every appliance with a motor or a compressor has two power numbers:
- Running watts — what it draws once it's going.
- Starting watts (surge) — the burst it demands for a second or two at startup, while the motor gets itself moving.
For anything with a compressor, that burst is several times the running number. Our generator sizing tool's own table tells the story:
| Appliance | Running watts | Starting watts |
|---|---|---|
| Refrigerator / freezer | 150 | 600 |
| Sump pump (1/2 HP) | 800 | 1,300 |
| Well pump (1/2 HP) | 750 | 1,400 |
| Phone charging | 30 | 30 |
Four times the running draw for the fridge, gone in a blink — but very real to the battery that has to survive it.
Your backup power source has to survive the tallest spike, not the average. A power station that comfortably covers 400 watts of running load will still shut itself off when a 600-watt startup surge lands on it.
Where to find your numbers
You don't have to guess:
- The label on the appliance. Usually a plate or sticker inside the fridge door, on the back panel, or near the plug. It lists watts, or volts and amps (volts × amps = watts).
- The yellow EnergyGuide sticker on newer appliances gives yearly energy use — useful for comparing, less useful for surge. The nameplate is the number that matters here.
- Our sizing tool carries honest defaults for the common household loads, so you can build the whole picture in a minute without a flashlight and a notepad.
The quiet good news
Two things work in your favor. First, the surge lasts a second or two — batteries rate a separate "peak" number for exactly this, so check that spec when you compare. Second, a fridge doesn't run constantly; the compressor cycles on and off, which is why a modest battery can carry one much longer than the label math suggests.
Plan for the spike, and the rest of the plan gets easier. Our generator and battery sizing tool does the adding — and the surge-checking — for you.