CPAP battery backup calculator: watts, hours and nights
Calculate an energy scenario from your CPAP's documented average draw, session duration, reserve and losses. Check power compatibility separately with the device supplier.
There is no universal “CPAP battery size.” Enter the average draw for your exact device, adapter and normal settings. A battery with enough watt-hours may still have the wrong voltage, connector, transfer behavior or approved power path. This worksheet does not establish safe or uninterrupted therapy.
Your scenario
Enable JavaScript and enter documented operating watts to calculate.
Inputs stay in this page. Nothing is sent to a server or saved automatically. The download is a local arithmetic worksheet, not a product compatibility approval.
Use operating watts, not the adapter rating
ResMed's cited AirSense 11 ANZ user guide lists a 65W power supply, typical power consumption of 56.1W and peak consumption of 73.2W. They are different specifications. The published typical figure is a reference under the maker's conditions, not a measurement of your device in your bedroom. Confirm the exact regional model and setup, including humidification and heated tubing, with its supplier.
A reference calculation, not a device-runtime promise
Using 56.1W as a documented reference scenario for eight hours gives 448.8Wh at the load. At an assumed 85% delivery efficiency and zero additional standby, that requires 528Wh of nominal storage for one session. Deliberately retaining 20% of charge raises the arithmetic to 660Wh. Neither figure certifies a particular battery or says that your prescribed setup draws 56.1W.
| Entered average draw | 8-hour load energy | Nominal Wh at 85%, no retained reserve |
|---|---|---|
| 20W hypothetical | 160Wh | 188.2Wh |
| 40W hypothetical | 320Wh | 376.5Wh |
| 56.1W published reference | 448.8Wh | 528Wh |
What counts as a complete night?
The result divides modeled available energy by the energy for the session length you entered and rounds down to complete sessions. It assumes the battery powers only this setup during those sessions, with outputs off between them and no recharging. Standby is counted for the entered operating hours only. If a station is left on for the whole outage, include those extra hours in the household planner.
Confirm the power arrangement before relying on it
- Ask the supplier about the exact device, approved battery or converter, voltage, connector and waveform.
- Confirm whether a claimed backup/UPS mode has a transfer interruption that the device tolerates.
- Plan around battery health, temperature and the real draw at your normal prescribed settings.
- Do not change therapy settings, humidification or prescribed use to make this calculator's result fit.
Agree a power-outage plan with your care team and equipment supplier. This CPAP worksheet is not intended to plan life-support or ventilator backup and provides no medical recommendation.
Include other household loads in the outage planner →
Sources and scope
- ResMed AirSense 11 user guide, ANZ edition: technical specifications
- ResMed: should I get a CPAP battery?
Documentation reviewed October 24, 2026. Manufacturer ratings are source claims, not our equipment tests. Numeric examples are calculations under stated assumptions. No device, pump, battery, transfer switch or installation is certified by this tool.