CPAP Battery Calculator
Pick your CPAP setup and your battery or power station. The calculator shows how many hours and nights it will run your machine, and the capacity you need for the number of nights you want to cover.
Assumptions: 85% efficiency through the AC outlet and power brick, 92% with a DC cord; LiFePO4 batteries used to 95% of their capacity, AGM batteries to 50% to protect their lifespan. Cold weather can cut battery capacity by 10–20% or more. This is an estimate for planning, not medical advice: always follow your doctor's and equipment provider's guidance for your therapy settings.
Typical CPAP power draw
CPAP consumption depends far more on heat than on the machine itself. These ranges are starting points; your pressure setting, room temperature and model all change them.
| Setup | Typical average draw | Energy for an 8-hour night |
|---|---|---|
| No humidifier | 30–60 W | 240–480 Wh |
| Heated humidifier on | 60–90 W | 480–720 Wh |
| Humidifier + heated tube | 100–150 W | 800–1,200 Wh |
The top of that last range is not theoretical: an RV owner who metered a ResMed AirSense 10 overnight with the heated humidifier and heated tube measured about 1.17 kWh over 8 hours (RV Electricity). If you use heat, measure your own machine before you buy a battery.
How the calculator works
Runtime (hours) = usable battery energy × efficiency ÷ CPAP watts.
- Usable energy: a power station's rated watt-hours; a 12V LiFePO4 battery's Ah × 12.8 V × 95%; a 12V AGM battery's Ah × 12 V × 50%, because draining lead-acid further shortens its life.
- Efficiency: 85% through the AC outlet and your CPAP's power brick, 92% with a DC cord.
- Nights: runtime divided by your hours of sleep.
For the full method and a runtime chart, read How Long Will a Portable Power Station Run a CPAP?
Choosing a battery for your CPAP
For most people, a LiFePO4 power station of around 1,000 Wh covers two or more nights without heat and about one night with the humidifier. If you want it plugged in every night as automatic backup, look for a fast UPS switchover (10 ms or less). Our shortlist and the trade-offs are in Best Portable Power Station for CPAP.
FAQ
- How do I find my CPAP's real power draw?
- Plug the CPAP into a plug-in energy meter for one night with your usual settings. Divide the watt-hours it shows by the hours you slept to get your average watts. Many power stations also show the live wattage on their screen. The number printed on the power brick is the maximum, not what the machine uses all night.
- Why does the heated tube make such a difference?
- Heating the air and the hose takes far more energy than running the blower. Owners who have metered their machines report average draws several times higher with the heated humidifier and heated tube on than with heat off.
- Is a DC cord worth buying?
- Usually, yes. Running through the AC outlet converts battery power to AC and then back to DC in the CPAP power brick, losing energy twice. A DC cord or converter made for your CPAP model skips that, which adds about 8% more runtime in this calculator.
- Can I use a car battery or a trolling motor battery?
- A deep-cycle battery works; a car starting battery is not designed for being drained overnight and wears out quickly. Choose AGM or LiFePO4 in the calculator to see the difference: you can only use about half of an AGM battery without shortening its life.
This tool is about power, not therapy. Always follow your doctor's and equipment provider's advice for your CPAP settings.