Free CPAP tool
CPAP Battery Runtime Calculator
Enter your battery's watt-hour rating, how much power your machine draws with and without the humidifier, and how the battery connects. You get usable watt-hours, hours of runtime and nights of sleep. The humidifier is usually the biggest power user, so try both settings.
Formula
Energy delivered = battery Wh x usable share x conversion efficiency. Runtime in hours = energy delivered / average watts. Nights = runtime / hours of sleep.
The humidifier toggle picks which wattage is used. The default humidifier-on figure, 56.1 W, is the typical power consumption ResMed lists for the AirSense 11 power supply in the user guide, which makes it a conservative ceiling. The 10 W humidifier-off default is only an example. Your real draw depends on your pressure, the room temperature, and your humidity and tube settings, so the best number is one you measure with a plug-in power meter or take from your machine's battery guide.
Worked example
A 99 Wh battery, humidifier off at 10 W, 90% usable, 85% efficiency, 8 hours of sleep: energy delivered = 99 x 0.90 x 0.85 = 75.7 Wh. Runtime = 75.7 / 10 = 7.57 hours, which is 0.95 nights. Switch the humidifier on (56.1 W) and runtime drops to 75.7 / 56.1 = 1.35 hours. Plug the same battery in through a DC cable at about 100% efficiency and humidifier-off runtime rises to 89.1 / 10 = 8.91 hours.
Assumptions and limits
- Draw is treated as a steady average; real draw rises with pressure and humidifier heat.
- The 10 W humidifier-off default is an illustration, not a measured figure for any model.
- Usable capacity and efficiency defaults are planning assumptions. A retailer guide says a 12 V inverter setup can lose 30 to 40% of battery life to heat, so a DC cable or DC converter usually runs longer.
- Batteries lose capacity in the cold and as they age.
Supplies that can help
A battery pack that runs a CPAP machine without mains power, for camping, power outages or long flights.
A cord or converter that runs a CPAP from a 12 V or 24 V DC source, such as a car outlet, RV or deep cycle …
A heat and moisture exchanger (HME) that captures warmth and moisture from your breath and returns it on the next breath, used mostly with travel CPAPs …
A padded bag that protects the machine, mask, tubing and power supply in transit.
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Frequently asked questions
Why does my CPAP battery die so fast with the humidifier on?
Heating water and a heated tube takes far more power than running the blower. ResMed lists 56.1 W typical consumption for the AirSense 11 power supply, while blower-only use is a fraction of that. Turning the humidifier off, or using a heat-and-moisture exchanger, is the usual way to stretch a battery.
Should I use an inverter or a DC cord with a CPAP battery?
A DC cord or the maker's DC converter avoids the loss of converting DC to AC and back. That loss is why inverter setups run for noticeably fewer hours on the same battery. Use the cable your machine's maker approves.
How many watt-hours do I need for one night?
Multiply your machine's average watts by hours of sleep, then divide by efficiency. At 10 W for 8 hours through an 85% efficient inverter, that is about 94 Wh, before adding any reserve. With the humidifier on you may need several times more.
Can I take this battery on a plane?
Under FAA rules, lithium-ion batteries up to 100 Wh are allowed in carry-on, 101 to 160 Wh need airline approval with a limit of two spares, and over 160 Wh are forbidden. Use the FAA battery watt-hour check calculator to confirm your battery's rating.
Sources
Last reviewed October 11, 2026. How we research · Report an error