Portable power station runtime calculator

Quick answer

Runtime is an energy calculation. Compatibility is a different question. A battery can have enough watt-hours for a load and still be unable to run it because the inverter output is too low, the starting surge is too high, or the load needs 240 V.

This calculator intentionally does not assume one universal inverter-efficiency percentage, refrigerator duty cycle, motor-start multiplier, or battery reserve. Those numbers vary by station, load, operating mode, and conditions. Use measurements or exact manufacturer data when you have them.

How the revised calculation works

The simple model is:

• Energy basis = measured delivered Wh if you have it; otherwise rated battery Wh
• Planning energy = energy basis × (1 − any headroom you deliberately choose)
• Average device load = running watts × duty cycle + off-cycle watts × off-cycle share
• Average system load = average device load + measured station/inverter idle watts
• Estimated runtime = planning energy ÷ average system load

If you only enter rated battery capacity, treat the result as an upper-bound planning estimate. The station cannot normally deliver every rated watt-hour to an AC appliance because conversion losses, internal consumption, battery-management cutoffs, temperature, and battery condition all matter.

Get better inputs

• Rated Wh: use the official specification or manual for the exact station.
• Delivered Wh: best obtained from a controlled discharge test for the output path you plan to use.
• Running watts: for ordinary plug-in 120 V equipment, a suitable plug-in energy meter can measure actual draw over time.
• Duty cycle: for cycling equipment, measure how long the device actually runs during a representative period rather than assuming a generic percentage.
• Idle draw: low-power AC loads can be materially affected by the station's inverter self-consumption. Enter it only when you have a credible specification or measurement.
• Starting watts: compressors, pumps, and motors may need substantially more power during startup. Use measured or manufacturer data rather than a universal multiplier.

Runtime does not prove compatibility

Before relying on the runtime result, check three separate limits:

1. Continuous output: the station must support the load while it is running.
2. Starting or surge output: motor and compressor loads must start without tripping the inverter. Also check how long the manufacturer says its surge rating can be sustained.
3. Voltage: a 120 V-only station cannot run a 240 V appliance just because it has enough Wh or headline watts.

Why the old appliance presets are gone

“A fridge is 150 W at a 33% duty cycle” or “a CPAP is 60 W” is convenient, but it is not a reliable universal input. Refrigerator compressors, room temperature, door openings, defrost cycles, CPAP pressure and humidification settings, networking hardware, and air-cleaner fan speeds all vary. The calculator now asks for the exact load instead of silently inventing one.

For CPAP or other medical-adjacent equipment, follow the device manufacturer's backup-power guidance and confirm your exact configuration rather than relying on a generic preset.

Cold-weather and battery-condition caveats

A room-temperature calculation is not a winter guarantee. Health Canada advises bringing larger lithium-ion battery systems to room temperature before use and says not to attempt charging below 0°C. The exact operating and charging limits for a portable power station come from that model's manual.

When this calculator is the wrong tool

• Use the fridge/freezer outage calculator for food-safety timing.
• Use the internet outage guide for modem/router/ONT architecture.
• Use the furnace outage guide for furnace-specific electrical and connection issues.
• Use the sump-pump backup guide for pump cycling, surge, and failure-path planning.
• Use the generator size calculator when your required loads exceed practical portable-station limits or need longer-duration fuel-based backup.

Canadian certification

Health Canada says electrical products that plug into an outlet must meet Canadian national safety standards and be certified by an accredited certification body. Look for a recognized Canadian certification mark such as CSA, cUL, or cETL on the product, and verify the exact model rather than relying on a marketplace listing alone.