The formula
Energy per night (Wh) = (CPAP watts + Humidifier watts) × Hours ÷ Efficiency
Nights = Battery Wh × Usable % ÷ Energy per night
Tips for longer battery life
- Use a DC power cord made for your machine. Running the mains power supply through an inverter wastes 10–15%.
- Turn off the heated humidifier and heated tube if you can. They often use more power than the CPAP itself.
- Lower pressure settings use less power. Your average power on a battery is usually well below the power supply's rating.
- The power supply brick's rating (for example 90 W) is a maximum, not what the machine normally uses.
This is a planning estimate, not medical advice. Ask your equipment supplier about battery operation for your specific machine.
Frequently asked questions
How long will a 500Wh power station run a CPAP?
Without the humidifier, a CPAP using 30–40 W runs about 10–14 hours from a 500 Wh unit on DC, so roughly 1.5 nights. With heated humidification, often less than one night.
Can I run a CPAP from a car battery?
Yes, with a DC cord, but a lead-acid car battery should only be discharged about 50%, and starting the car afterwards may be a problem. A separate leisure or lithium battery is better.