How to Calculate Power Station Runtime

A runtime estimate begins with usable battery energy, not the capacity number alone.

The basic formula

Use this sequence:

Convert inverter efficiency to a decimal.
Convert the reserved battery percentage to the available percentage.
Multiply rated capacity by efficiency and available percentage.
Divide usable energy by the appliance’s average load.

usable energy =
battery capacity × inverter efficiency × available battery percentage

runtime =
usable energy ÷ average appliance wattage

For a 1,000 Wh battery, 85% efficiency, and a 10% reserve:

1,000 Wh × 0.85 × 0.90 = 765 Wh usable energy

A steady 100 W load would have an estimated runtime of:

765 Wh ÷ 100 W = 7.65 hours

This is an editorial estimate, not a tested result for a specific product.

Rated capacity is not usable capacity

Rated capacity is the energy stored under defined conditions. AC appliances receive less because the inverter and internal electronics consume energy. Manufacturers may also reserve part of the battery to protect it.

If an independent usable-capacity test is available for the exact model and operating mode, use that value instead of estimating losses twice.

Account for appliance cycling

Refrigerators, pumps, and some heating or cooling appliances cycle on and off. Duty cycle estimates the portion of time the appliance draws its running power.

average load = running watts × duty cycle

A 200 W appliance operating half the time has an estimated average load of 100 W. Real cycling changes with temperature, settings, door openings, and the condition of the appliance.

Check output before runtime

Runtime is irrelevant if the power station cannot start or continuously support the appliance. Compare:

Continuous AC output with the appliance’s running watts
Surge capability with startup demand
Outlet voltage and frequency
Manufacturer restrictions for medical, heating, or motor loads

Use a conservative result

The EcoFriendlyGuide calculator shows a second estimate that is 15% below the formula result. This is a planning margin, not a universal engineering constant. Cold conditions, battery age, standby losses, and high-load operation can reduce runtime further.

Calculate your scenario

Open the power station runtime calculator to edit capacity, appliance watts, efficiency, reserve, and duty cycle.