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CPAP battery runtime calculator
Estimate how many nights a power station or battery will run a CPAP machine, with or without the heated humidifier, on DC or AC power.
Results
| Nights per full charge | 2.1 nights |
|---|---|
| Battery energy used per night | 222 Wh |
| Total runtime | 16.6 hours |
- Turning off the heated humidifier and heated tube is the single biggest way to extend battery runtime.
- A CPAP is a medical device. Follow your physician's and manufacturer's guidance, and keep a backup plan for long outages.
About this calculator
For CPAP users, a power outage or a camping trip raises one question: will the battery make it through the night? The answer depends far more on the heated humidifier than on the machine itself. A CPAP's blower typically draws a modest 15-30 W, but the humidifier and heated tube can double or triple that.
This calculator estimates nights per charge for any battery or power station. It compares the efficient DC path (the CPAP maker's DC cord) with plugging into an AC outlet, which pays inverter losses and idle draw all night.
How to use it
- Enter your CPAP's average power. If you can, measure a full night with a plug-in meter and divide the Wh by the hours.
- Enter how many hours you use it per night.
- Choose DC or AC. The DC path needs the manufacturer's DC cable or converter for your model.
- Enter your battery or power station's rated Wh.
The formula
DC per night = CPAP W × hours ÷ converter efficiency.
AC per night = (CPAP W ÷ inverter efficiency + idle W) × hours.
Nights = (capacity × usable %) ÷ energy per night.
Worked example (default values)
Inputs
| CPAP average power | 25 W |
|---|---|
| Hours of use per night | 8 h |
| Power path | DC (CPAP maker's DC adapter / converter) |
| Battery capacity | 512 Wh |
| Usable share | 90 % |
| DC converter efficiency | 90 % |
| Inverter efficiency | 88 % |
| Inverter idle draw (AC only) | 10 W |
Results
| Nights per full charge | 2.1 nights |
|---|---|
| Battery energy used per night | 222 Wh |
| Total runtime | 16.6 hours |
Tips and common mistakes
Pressure matters too. Higher prescribed pressures make the blower work harder. Two people with the same machine can see different draws. Measuring your own is best.
For multi-day outages, a small solar panel (100-200 W) can usually replace a night's CPAP use in a few hours of sun. Check with the solar charging time calculator.
Frequently asked questions
How long will a 500Wh battery run a CPAP?
Without the humidifier on DC, about 2 nights at 25 W for 8 hours. With the heated humidifier on AC, it may last only one night.
Can I run a CPAP from a power station?
Yes. A pure sine wave AC outlet works with any CPAP, and the DC route is more efficient if your manufacturer offers a DC cord.
Do I need a special battery for a CPAP?
No. Any power station or battery with the right output works. Some CPAP makers sell their own batteries, but generic LiFePO4 power stations are common and often cheaper per Wh.
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Estimates for planning only, based on the assumptions shown. Real-world performance varies with equipment, temperature and installation. Updated October 19, 2026. See our methodology.