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Battery runtime

How long will the battery last?

Three numbers: how big the bank is, how much of it you're willing to use, and what's running. The chart shows the charge falling hour by hour.

By James JonesUpdated

01 The bank

Wh

Amp-hours × nominal volts. A 12 V 100 Ah lithium battery is about 1,280 Wh.

Or start from a Vatrer size

02 How deep you'll go

%

Set this from your battery's spec sheet. The page doesn't assume a chemistry for you.

03 What's running

W

Read it off a battery monitor or add up nameplate watts of what's on.

Runtime at this load

0hours

  • State of charge
  • Your usable floor

How the math works

Hours = battery watt-hours × the usable share ÷ load watts. A 3,840 Wh bank, 80% usable, running 150 W lasts 20.5 hours.

The line is straight because the load is steady. Real nights aren't. A furnace blower cycling on and the fridge kicking in will bend it. Use the average from a battery monitor if you have one.

What it leaves out

Inverter losses, cold-weather capacity, and the battery's age. If you're running AC loads through an inverter, the battery sees more than the appliance label says.