How Big a Battery Do You Need for a Power Outage?
Updated 2026-09-26
For home backup, the question isn't "how many watts?" — it's "how many watt-hours per day, for how many days?" Here's a quick way to work it out. The home backup planner does the same math for your own list of appliances.
Step 1: Add up a day of the essentials
Multiply each appliance's running watts by the hours it actually runs. Fridges and freezers cycle on and off, so they use far less than their rating suggests.
| Appliance | Typical draw | Energy per day |
|---|---|---|
| Full-size refrigerator (runs ~35% of the time) | 150W | ~1.3kWh |
| Chest freezer (runs ~40% of the time) | 80W | ~0.8kWh |
| Wi-Fi router + modem, 24 hours | 20W | ~0.5kWh |
| CPAP, 8 hours (no humidifier) | 40W | ~0.3kWh |
| 4 LED bulbs, 6 hours | 40W | ~0.25kWh |
| Phones and a laptop | — | ~0.2kWh |
These are typical figures, not measurements of your appliances. A plug-in watt meter or the label on the back gives better numbers.
That gives three rough tiers:
- Bare essentials (fridge, Wi-Fi, phones, a few lights): about 2kWh a day.
- Essentials + freezer + CPAP: about 3.3kWh a day.
- Add cooking, a window AC or a well pump and it climbs fast. A microwave or kettle uses little energy in short bursts, but an AC or well pump can add several kWh a day (see can a power station run a well pump?).
Step 2: Allow for losses
A power station's inverter loses roughly 10–15% converting battery power to AC. Plan on getting about 85% of the rated capacity as usable AC power.
Step 3: Multiply by the days you want to cover
Most outages are short, but storms can knock power out for days. Here's roughly what one charge covers at 85% usable:
| Battery capacity | Bare essentials (2kWh/day) | Essentials + freezer + CPAP (3.3kWh/day) |
|---|---|---|
| 2,048Wh | ~0.9 days | ~0.5 days |
| 3,840Wh | ~1.6 days | ~1 day |
| 6,144Wh | ~2.6 days | ~1.6 days |
| 10,000Wh (station + add-on batteries) | ~4 days | ~2.6 days |
Bigger battery, or solar?
Beyond a day or two, recharging usually beats more storage. A few hundred watts of solar on a decent day can put back 1–2kWh, enough to cover a bare-essentials load indefinitely in good weather. See how many solar panels you need.
Add-on batteries make sense when you need multi-day coverage without sun, or you want to run heavier loads. Most home-class stations take them: the Anker SOLIX F3800 Plus (3,840Wh, expandable to 53.8kWh), EcoFlow DELTA Pro 3 (4,096Wh, to 48kWh) and Jackery HomePower 3600 Plus (3,584Wh, to 21kWh). The BLUETTI Apex 300 starts smaller at 2,765Wh and expands to 58kWh.
Don't forget output and voltage
Capacity decides how long; output decides what you can run. Starting a fridge, freezer or pump takes a surge several times its running draw. Well pumps and many other hardwired loads are 240V. A station that connects to your home's circuits needs a transfer switch or inlet installed by a licensed electrician.
Quick answer
- Keep the fridge, Wi-Fi and phones going overnight: 2kWh-class station.
- A full day of essentials, including a freezer or CPAP: 3.5–4kWh.
- Multi-day outages: 4kWh or more plus solar, or add-on batteries.
Try your own numbers in the home backup planner, or compare every model in the home backup class.