Home Battery Backup Sizing Calculator
Figure out how much home battery backup you need to keep the essentials running during an outage. Enter the energy you want to back up per day and how many days of autonomy you want, and this home battery sizing calculator finds the storage capacity (nameplate) you need after usable depth of discharge and round-trip losses.
Battery capacity to buy
12.3 kWh
10.0 kWh usable energy needed
≈ 0.9 units of 13.5 kWh
Nameplate capacity accounts for usable depth of discharge and round-trip losses, so it runs higher than the raw energy you want to cover. The 13.5 kWh unit is a generic reference size, not a specific product. To keep a battery affordable, back up only the essentials (fridge, lights, Wi-Fi, a few outlets) rather than the whole home. Estimate only.
Portable battery backup
If the essentials above fit in a few kilowatt-hours, a portable power station covers them without a permanent install. The larger unit can feed real circuits through a transfer switch installed by an electrician.
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2 kWh class
Bluetti Elite 200 V2
Best for: Most capacity and battery longevity per dollar in the 2 kWh class
Whole-circuit class
EcoFlow DELTA Pro 3
Best for: Backing up real circuits (furnace, well pump, kitchen) without fuel
Frequently asked questions
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That capacity figure is what to shop by. Portable power stations are the same battery chemistry in a smaller, movable package. See the portable power station picks.
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Sources & standards
This tool's methodology and data follow US standards and authoritative public datasets: