Outage cooling backup
Estimate how long a portable power station can run a window or portable air conditioner, what battery size you need, and whether continuous output and startup surge appear compatible.
Air conditioners are heavy motor loads. Battery Wh controls cooling time, while continuous AC output and surge output determine whether the station may actually run and start the compressor.
Presets are planning values. Use the EnergyGuide label, model specifications, nameplate, or measured watts when available. Planning example for a small room air conditioner. Use your EnergyGuide label or nameplate when available.
A 70% duty cycle means the compressor runs about 42 minutes per hour. Hot rooms, direct sun, poor insulation, and undersized units can push duty cycle higher.
These examples use a 1000Wh power station at 100% charge, 95% battery health, 10% reserve, and 88% inverter efficiency. Presets are planning values; actual runtime depends on model, temperature, duty cycle, insulation, and compressor behavior.
| AC preset | Cooling capacity | Running watts | Startup surge | Duty cycle | 1000Wh runtime |
|---|---|---|---|---|---|
| Small window AC 5,000 BTU | 5,000 BTU/h | 500 W | 1500 W | 70% | 2 hr 9 min |
| Window AC 8,000 BTU | 8,000 BTU/h | 800 W | 2400 W | 70% | 1 hr 21 min |
| Large window AC 12,000 BTU | 12,000 BTU/h | 1200 W | 3600 W | 75% | 50 min |
| Portable AC 8,000 BTU | 8,000 BTU/h | 1067 W | 3200 W | 75% | 56 min |
| Portable AC 10,000 BTU | 10,000 BTU/h | 1333 W | 4000 W | 75% | 45 min |
Running watts depend on BTU capacity, efficiency rating, compressor design, fan speed, and room conditions. If you know BTU/h and CEER or EER, watts can be estimated as BTU/h divided by the efficiency ratio.
An AC may not draw compressor power every minute. Once the room reaches set temperature, it can cycle on and off. Hot rooms, poor insulation, direct sun, and undersized units can push duty cycle close to continuous.
Compressor startup can require a short surge above running watts. Surge is checked separately because it should not be counted as continuous energy use.
Portable units often have different efficiency behavior than window units. Use SACC, CEER, EnergyGuide, or measured watts for your specific model instead of treating every BTU rating the same.
Check battery Wh, continuous output, surge output, and AC outlet limitations. Many small power stations may run lights or routers easily but fail on compressor startup.
Cooling plus a refrigerator, freezer, router, CPAP, or sump pump can quickly exceed capacity. Add those loads separately in the main calculator.
Sometimes. A small efficient window AC may work with a large enough station, but the station must meet battery capacity, continuous output, and startup surge requirements.
It depends on running watts, duty cycle, inverter efficiency, and battery reserve. A small 500W unit at a 70% duty cycle averages about 350W before battery losses, so runtime may be only a few hours.
If the label lists CEER or EER, divide BTU per hour by that efficiency ratio. For example, 8000 BTU/h at CEER 10 is about 800 W running.
Many compressor AC units do. Inverter or soft-start models can behave differently, so confirm the manufacturer specifications or measured startup behavior.
Start with the AC running watts, duty cycle, desired cooling hours, and startup surge. The calculator estimates Wh needs and checks output compatibility.
This page is intended for plug-in room, window, and portable AC units. Central HVAC systems usually require professional electrical planning and are often beyond portable power station capability.
Results are estimates. Actual air-conditioner runtime can vary with outdoor temperature, room size, insulation, sun exposure, humidity, thermostat set point, compressor cycling, battery age, inverter idle draw, and manufacturer startup behavior.
For mixed outage loads, use the main power station runtime calculator, or compare specialized calculators for sump pump backup, freezer backup, and Starlink runtime.