Battery runtime calculator

Enter the battery as amp-hours and volts, or as kWh, choose the chemistry, and enter the load. The calculator applies depth of discharge and inverter efficiency and returns the hours the battery will actually run that load.

Updated 16 September 2026

Inputs

Battery entered as

Capacity

Voltage

Number of these batteries

Series adds volts; parallel adds Ah; total energy is the same either way.

Chemistry

Depth of discharge

Overridden by the chemistry unless Custom.

Inverter efficiency

90–94% for modern units at moderate load.

Load

Average running watts; use duty-cycled averages for fridges and ACs.

Starting state of charge

Results

Nominal energy

—

kWh on the label

Usable energy

—

kWh after DoD

Delivered to loads

—

kWh after inverter

Runtime

—

hours at this load

At 200 W

—

lights, fans, TV

At 1,000 W

—

with an inverter AC

Formulas and assumptions

E_nominal = Ah × V × n ÷ 1000
E_usable = E_nominal × DoD × SoC
E_delivered = E_usable × η_inverter
Hours = E_delivered ÷ Load_kW

Lead-acid capacity falls further at high discharge rates (Peukert effect) and in heat; treat lead-acid results above 0.2C (load W > Ah × V ÷ 5) as optimistic. Lithium packs hold their rating up to the BMS current limit.

What this is

An estimate from stated formulas and typical values, for planning and for checking quotations. It is not an engineering design, does not replace a load audit and site survey by a qualified installer, and does not account for shading, roof orientation, cable losses or local standards. ZEUS is not an engineering firm.