CPAP Battery Calculator: How Many Nights Will It Last?
Medical note: This calculator estimates power use and battery runtime only. It isn’t medical advice. Don’t change your CPAP settings (including the humidifier) to save battery without talking to your doctor or equipment provider, and check your device maker’s guidance on battery use.
Nights = battery Wh × efficiency ÷ (CPAP watts × hours per night). ResMed measured its AirSense 10 at about 7 W without the humidifier, 22 W with it and 34 W with the humidifier and a heated tube. On a 1,000 Wh station through a DC converter, that’s about 16 nights, 5 nights or 3.3 nights of 8 hours. Enter your own numbers below.
Presets: ResMed’s measured averages for the AirSense 10.
Use the average draw, not the power supply’s rating; see the notes below.
The numbers behind the presets
ResMed published the power its AirSense 10 AutoSet used in a lab test, run with a breathing simulator at 8–15 cm H2O pressure. We read its "watt hour" figures as watt-hours per hour of use, which is the same as average watts:
| AirSense 10 setup | Average watts | One 8-hour night |
|---|---|---|
| Standby | 5 W | – |
| Machine only, no humidifier | 7 W | 56 Wh |
| With humidifier | 22 W | 176 Wh |
| With humidifier and heated tube (ClimateLineAir) | 34 W | 272 Wh |
The humidifier is the big variable: it more than triples the energy per night. Your own numbers depend on your pressure, humidity and room temperature, so treat these as a starting point. Our CPAP guide explains the test and what changes the result.
Why the power supply's watts give the wrong answer
The label on a CPAP power supply shows its maximum rating, not what the machine uses on an average night. ResMed's AirSense 11 user guide, for example, lists its 65 W power supply at 56.1 W typical and 73.2 W peak consumption. Using those numbers would make a battery look like it lasts a fraction of what it really does. Use your device maker's published average if it has one, or the presets above for a ResMed AirSense 10.
DC converter or AC outlet?
ResMed's battery guide strongly recommends powering its devices from a battery through a DC-to-DC converter rather than an inverter, because converters are more efficient and add protections. The calculator uses 90% efficiency for the DC option and 85% for the AC outlet; both are our planning assumptions, not measured values for any model. Use the DC cable or converter your CPAP maker sells for your model.
The 20% margin
The checkbox removes 20% of the usable energy. That's our rule of thumb for battery aging, cold nights and settings that use more than the lab test. For a medical device, we suggest leaving it on.
Quick reference: nights on common station sizes
With the DC converter (90%), 8-hour nights and no margin:
| Station capacity | No humidifier (7 W) | With humidifier (22 W) | Humidifier + heated tube (34 W) |
|---|---|---|---|
| 288 Wh (small, like those in our 300 Wh comparison) | 4.6 nights | 1.5 nights | 0.9 nights |
| 1,024 Wh | 16.5 nights | 5.2 nights | 3.4 nights |
| 2,048 Wh | 32.9 nights | 10.5 nights | 6.8 nights |
For devices other than a CPAP, use our runtime calculator. If you're planning for outages, our home backup guide adds the fridge and router to the list.
Safety: Follow your CPAP maker's instructions for battery and DC use, and use only the cables and converters it approves. If you rely on CPAP therapy, talk to your doctor and equipment provider about a backup plan for outages. Never run a fuel generator indoors to power medical equipment: carbon monoxide can kill in minutes.
To see where our numbers come from, read How We Research.
