PowerCalcLab

Inverter calculator

Portable Power Station Runtime Calculator

Estimate how long a portable power station can run a load without assuming every advertised watt-hour reaches the outlet. Capacity and output-power checks are shown separately.

Advanced assumptions

Results update as you type. The calculator runs entirely in your browser — nothing you enter is sent anywhere.

Estimated runtime5 h 34 min

Calculation breakdown

Available battery energy90% charge window at 90% health829 Wh
Battery-side power149.2 W
Modeled delivered energy705 Wh
Continuous output checkEntered station limit: 1800 WPass
Runtime = rated Wh × charge window × health ÷ (load W ÷ output efficiency + overhead W)
= 1024 × 0.9 × 0.9 ÷ (120 ÷ 0.85 + 8)
= 5.56 h = 5 h 34 min
  • Rated capacity is not the same as energy delivered at an outlet. Reserve, aging, conversion loss and output electronics all reduce runtime.
  • Cycling appliances need an average measured load for runtime and their startup power checked against the station's surge specification.

Method

How the number is reached

The usable charge window and battery health reduce the station's rated watt-hours. The connected load is converted back to battery-side watts using the entered output efficiency, then output electronics overhead is added.

Manufacturers publish battery capacity and output-port power as different specifications. A station can contain enough energy for a task yet still be unable to start or continuously power the appliance.

Available battery Wh = rated Wh × (starting charge − reserve) × health
Battery W = load W ÷ output efficiency + output overhead W
Runtime h = available battery Wh ÷ battery W

Symbols

Wh
Stored energy in watt-hours

Worked examples

The same maths, applied

Example

1,024 Wh station running a 120 W load

Start at 100%, keep 10% reserve, assume 90% health, 85% output efficiency and 8 W electronics overhead.

Available energy = 1,024 × 90% × 90% = 829.4 Wh
Battery power = 120 ÷ 85% + 8 = 149.2 W
Runtime = 829.4 ÷ 149.2 = 5.56 h

Result: About 5 h 34 min.

Limits of the model

What it assumes, and where it stops

Assumptions

The entered load is a steady average and output efficiency represents the selected outlet type and load point.

Not covered

Does not model temperature, automatic output timeout, inverter startup behavior or manufacturer-specific battery cutoffs.

Sources

Where these figures come from

  • DELTA 2 Portable Power Station — User ManualEcoFlowManufacturer specifications that keep rated battery capacity, continuous AC output, surge output and individual DC-port limits separate.
  • Inverter Smart — Technical specificationsVictron EnergyManufacturer ratings that distinguish continuous watts, continuous VA, temperature derating, peak power, maximum efficiency and zero-load consumption.
  • SI UnitsNIST Office of Weights and MeasuresDefinitions of the volt, ampere, watt and joule used for the unit conventions on this site.

Next steps

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Last meaningful update: 2026-08-19. This date changes only when the model, the sources or the guidance change.