Backup power calculator
Your battery size, peak watts, and matching options in about 30 seconds.
1. What do you need to keep running?
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?
3. Your state (for rebates)
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.
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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
- Energy per day = for each appliance, typical running watts × quantity × hours per day. Typical running watts are the midpoint of the sourced range. Estimate
- Battery energy needed = energy per day × days ÷ 0.85. Assumption The 0.85 factor covers inverter losses and reserve capacity.
- 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.
- Power station match: continuous output ≥ total running watts and surge rating ≥ peak watts. "Covers" compares battery capacity with your need.
- Installed battery cost = capacity × $1,130–$1,159 per kWh (EnergySage). Estimate
- Generator size = running and peak watts, each rounded up to the next 500 W.
Full methodology and sources →
Backup power, before the next outage
A short email when it matters: outage-season prep checklists before summer storms and winter freezes, state and utility rebates that open, change, or run out of money, and real price drops on the power stations in our data.