How much backup battery power do you need?

Choose the appliances you want to keep running during an outage. We'll estimate the battery capacity and power output you'll need.

1. Choose your appliances

Nothing is selected yet. Add the appliances you need, then edit the estimates to match your equipment. Watts and daily use vary.

Choose an appliance above to start your plan.

2. How long do you need backup power?

24 hours is an editable planning assumption.

3. Do you already have a battery?

Battery capacity determines how long it runs. Output wattage determines which appliances it can power.

If startup duration is unknown, peak wattage alone cannot verify compatibility.

Advanced Settings — Optional

Most users can start with the clearly stated planning assumptions below. Change them only when you know your battery’s specifications.

Default assumes stored energy, 90% usable capacity and 85% conversion efficiency. If the label means AC-delivered energy, select that basis; do not apply those losses again. Unconfirmed labels prevent an exact compatibility claim.

Editable planning assumption; not a universal battery rating.

85% is an illustrative planning factor, not round-trip efficiency or a manufacturer guarantee.

Assumes a full battery unless changed; positions are within the usable energy window.

Default 0 means no additional reserve after the hardware-usable limit.

Default 0 excludes unmeasured system overhead. Blank means unknown. Do not add it again if measured overall efficiency includes it.

How the estimate works

Capacity, output and everyday appliance use

Battery capacity is stored energy: 1 kWh equals 1,000 Wh. Output watts describe how much equipment can run at once. Energy use = appliance watts × quantity × operating hours. Refrigerator and pump hours describe total time actually running, not the entire time plugged in. Daily hours are spread proportionally across your requested outage; short outages and heavy pump use can differ. Adjust actual outage on-hours in each appliance’s advanced details when known.

The initial planning estimate assumes 90% of stored capacity is usable, 85% conversion efficiency, a full starting charge, no additional reserve and no separate overhead. These are editable assumptions, not product specifications. Confirmed usable DC ratings skip the usable fraction. Confirmed AC-delivered ratings skip both capacity and conversion reductions, charge/reserve changes and extra overhead because those are already included in that delivered-energy measurement.

Runtime is a capacity-only estimate at the selected appliances’ average demand, not a schedule or a promise that equipment can run. Continuous output and startup capability are checked separately. One known motor starts while other selected units run; other unknown starts remain unknown. No motor multiplier is invented.

Limitations and sources

Wattage and cycling change with appliance model, weather and settings. Your measurements and manufacturer specifications take precedence. Check voltage, connectors, peak duration, battery/BMS/inverter limits and installation requirements separately; this tool does not establish that a battery connects to all household circuits. No wiring instructions, product guarantees, solar/weather simulation or financial payback. Confirm medical-device backup needs separately.

Editable running-watt estimates are planning illustrations informed by Honda’s approximate appliance guide and DOE energy-use examples. Daily hours, the 90%/85% planning factors and all generic appliance selections are explicit scenario assumptions, not source promises. Actual startup power is left unknown until you enter equipment data. PNNL explains efficiency boundaries.

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