# Battery Backup Runtime Calculator

Estimate steady AC backup hours from battery energy and an entered load.

[Open this tool](https://whatson.pk/runtime-calculator/)

Category: Solar & Battery

Battery energy and the AC load together set a rough steady backup duration. Nominal capacity alone does not tell you the usable hours.

Enter discharge, health and efficiency assumptions alongside the load. Compare the result with observed runtime as the battery and operating conditions change.

## Inputs and controls

* Bank nominal voltage (V). Allowed range: 0.1 to 2000
* Bank capacity (Ah). Allowed range: 0.01 to 10000000
* Usable depth of discharge (%). Allowed range: 0.01 to 100
* Inverter efficiency (%). Allowed range: 0.01 to 100
* Steady AC load (W). Allowed range: 0.01 to 10000000
* Inverter DC idle draw (W). Allowed range: 0 to 1000000

## How to use

* Enter bank nominal voltage, bank capacity and usable depth of discharge.

* Enter inverter efficiency, steady AC load and inverter DC idle draw.

* Select Calculate result. Read the returned values alongside the assumptions below before copying, exporting or acting on the result.


## Why use this tool

The energy reductions stay visible, helping explain why nominal watt hours are greater than usable AC output.


## Before relying on the result

Constant power estimate. Battery age, temperature, discharge rate, BMS cutoffs and inverter idle behaviour can change actual runtime. DoD is an input, not a chemistry recommendation.


## Tool limitations

Constant power estimate. Battery age, temperature, discharge rate, BMS cutoffs and inverter idle behaviour can change actual runtime. DoD is an input, not a chemistry recommendation.

## Questions

### Is the duration a guarantee?

No. Temperature, discharge rate, battery age, cutoffs and inverter behaviour can change actual runtime.

### What should I check before using Battery Backup Runtime Calculator?

Check Bank nominal voltage, Bank capacity, Usable depth of discharge and Inverter efficiency. Use the exact units shown beside the controls and replace any example values with your own inputs.

Source page last modified (UTC): 2026-10-01T18:56:35+00:00

This profile describes the tool. It does not execute it or supply a professional certification.