Skip to content
WattBills.com
Sign in Open calculators

Battery Runtime Calculator

Estimate how long a battery powers a load.

Inputs

Inputs and assumptions

Nameplate watts for Battery Runtime 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
$155.13
Energy per year
913 kWh
Share of average US home
8.7%
Cost per running hour
$0.085
Cost per day
$0.43
Energy per day
2.5 kWh
Cost per month
$12.75
Screening tool. Verify your utility tariff and equipment specs before deciding.

Frequently asked questions

How long will a battery last?

Divide usable watt-hours by load watts. A 1,000 Wh station at 200W runs about 5 hours.

What is usable vs rated capacity?

Lead-acid gives about 50 percent usable; lithium gives 80 to 100 percent. Enter usable watt-hours.

Does inverter efficiency matter?

Inverters lose 10 to 15 percent on AC loads. DC loads skip that penalty.

How does load size change runtime?

Halving the load more than doubles effective runtime on chemistries with Peukert losses.

Related calculators

Guides

01 What EV Charging Really Costs in 2026 02 Time-of-Use Rates Without the Confusion: Peak Hours and Bill Calculations

Related articles

01 What EV Charging Really Costs in 2026

Workspace

Every result shows its math: your inputs, the formula, the numbers.

Save this calculation to return to the inputs, result, and report from your private workspace.

Sign in to save Create account

Sign in or create an account to save this calculation.