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Battery Capacity Calculator

Size battery capacity (kWh) for a backup need.

Inputs

Inputs and assumptions

Nameplate watts for Battery Capacity Calculator.

How many of this device you run.

Hours per day

Fridges run 7; laundry may run 2-3.

Compressors and thermostats cycle; a fridge averages ~40%.

Rate

Result

Cost per year
$248.20
Energy per year
1,460 kWh
Share of average US home
13.9%
Cost per running hour
$0.170
Cost per day
$0.68
Energy per day
4.0 kWh
Cost per month
$20.40
Screening tool. Verify your utility tariff and equipment specs before deciding.

Frequently asked questions

What battery size do I need?

Multiply load watts by backup hours, divide by depth of discharge and inverter efficiency.

How do volts and amp-hours convert?

Watt-hours equals volts times amp-hours. A 12V 100Ah battery holds 1,200 Wh nominal.

Lithium vs lead-acid sizing?

Size lead-acid double for the same usable energy because only half is safely usable.

Should I add a margin?

Add 20 percent for degradation and cold weather, more for critical medical loads.

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