How Long Will a Battery Run a CPAP Machine? (Real Math)
Short answer: a CPAP itself sips power — about 30–60 W running, or roughly 0.25–0.4 kWh over an 8-hour night. Turn on the heated humidifier and heated tube and it can triple, to 60–110 W and ~0.5–0.9 kWh/night. There's no motor surge, so almost any power station can run one; the only question is how many nights.
| Battery (usable) | Nights, humidifier OFF | Nights, humidifier ON |
|---|---|---|
| 0.5 kWh | ~1–2 nights | ~1 night |
| 1 kWh | ~3 nights | ~1–2 nights |
| 2 kWh | ~5–6 nights | ~3 nights |
| 5 kWh | ~2 weeks | ~1 week |
Assumes ~8 h/night, humidifier-off ~0.3 kWh and humidifier-on ~0.6 kWh, with ~85% AC-inverter losses already applied.
What moves the number
- The humidifier is the whole story. The blower is tiny; the heating element is what drains a battery. Turning off heated humidification (or running it on low) is the single biggest lever — it roughly doubles your nights.
- Use a DC cable if your machine offers one. Running the CPAP from the station's 12V DC output skips the inverter's ~10–15% conversion loss, adding runtime for free. Many ResMed/Philips units sell a dedicated DC cord.
- Pressure and altitude: higher prescribed pressures and auto-adjusting modes draw a little more; the effect is small next to the humidifier.
- Solar makes it indefinite: even a 100 W panel in modest sun replaces a humidifier-off night, so a 1–2 kWh station with one panel covers a multi-day outage.
Medical loads come first
If a CPAP — or oxygen concentrator, which draws far more (~300–600 W) — is essential, treat it as a non-negotiable load and size for the realistic outage in your area with margin. Talk to your equipment provider about a manufacturer battery and a DC cable, and don't rely on the intermittent tricks that work for a fridge. National outage context is in our backup power statistics (the average US home lost ~11 hours of power in 2024).
Add a CPAP to your other must-run loads in the battery size calculator, and see which power stations we'd actually buy for quiet bedroom use.
More runtime guides: refrigerator, well pump, and sump pump.