Outage Prep

Backup power calculator

Your battery size, peak watts, and matching options in about 30 seconds.

1. What do you need to keep running?

Will my backup last? Pick a scenario:
Quick start:
150–400 W
100–500 W
300–800 W
500–800 W
800–1050 W
750–1000 W
1000–2000 W
450–600 W
900–1200 W
3000–3500 W
1200–2400 W
600–1200 W
750–1500 W
3000–4500 W
500–1000 W
80–400 W
8–15 W
20–100 W
30–60 W
60–120 W
10–20 W
15–40 W
15–75 W

Wattage ranges: Champion Power Equipment wattage chart (as of 2026-10-25). Assumption Default "h/day" values are our estimates of how long each appliance actually draws power (e.g. a fridge compressor runs about 1/3 of the time = 8 h/day). Edit them to match your home. Not listed yet (no verified figures): EV Level 2 charging; Medical devices (oxygen concentrator etc.). For medical devices, use the watts on your device's label.

2. For how long?

24 hours

3. Your state (for rebates)

Battery energy needed
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Peak power (with surge)
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Assumption We divide by 0.85 to cover inverter losses and capacity you can't fully use. Running watts use the midpoint of each sourced range; peak uses the top of the range plus the single biggest motor start-up surge. Real-world use varies with weather, appliance age, and settings.

Will my backup last X days?

Capacities: brand/retailer listings in our data (each links its source, as of Oct 2026). Solar uses our stated assumption of 4 peak sun hours at 75% output; winter storms and hurricanes often bring clouds, so real recharge can be much lower. A station can't accept more solar than its input limit.

Assumption Scenario days are planning defaults you can change, not forecasts: winter storm and heat wave 3 days (Ready.gov advises supplies to "last for several days," Ready.gov kit, read 2026-10-28), wildfire shutoff 2 days, hurricane 1 week. Wattages are the same sourced ranges as the rest of the calculator. Winter storm guide →

How the math works

  1. Energy per day = for each appliance, typical running watts × quantity × hours per day. Typical running watts are the midpoint of the sourced range. Estimate
  2. Battery energy needed = energy per day × days ÷ 0.85. Assumption The 0.85 factor covers inverter losses and reserve capacity.
  3. Peak watts = the sum of each appliance's maximum running watts + the largest single start-up surge (starting watts − running watts). Motors rarely all start at the same moment, so we count only the biggest surge.
  4. Power station match: continuous output ≥ total running watts and surge rating ≥ peak watts. "Covers" compares battery capacity with your need.
  5. Installed battery cost = capacity × $1,130–$1,159 per kWh (EnergySage). Estimate
  6. Generator size = running and peak watts, each rounded up to the next 500 W.

Full methodology and sources →

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