Homelab and storage

UPS runtime

Estimate how long an uninterruptible power supply (UPS) will keep your equipment running.

Battery voltage (V)

Capacity per battery (Ah)

Number of batteries

Load (W)

Inverter efficiency: 85%

Usable from the battery: 80%

How many minutes do you want to bridge?

What does this mean?

The energy in a battery is voltage × capacity: a 12 V battery of 9 Ah contains 108 Wh. You cannot use all of that: the inverter loses energy and a lead-acid battery prefers not to be completely empty. Dividing by the consumption of your equipment gives the runtime.

This is an estimate. At high loads, lead-acid batteries deliver less than their stated capacity, and batteries age. For a server, calculate with a generous margin, and configure your server to shut down gracefully before the battery is empty.