Backup power for a CPAP
By our math, a 1,000 watt-hour box runs a 40-watt CPAP for about 21 hours, and a heated humidifier can shorten that.
By our math, a box that holds 1,000 watt-hours runs a 40-watt CPAP for about 21 hours. A heated humidifier or a heated tube uses more power, so your own time may be shorter. Watt-hours: how much power a box holds. Watts: how fast something uses power.
This page is about power, not health. Ask your doctor or equipment supplier if you depend on your machine.
The easy math
Our tools count 40 watts for a CPAP machine. Take the box size in watt-hours. Keep 85% of it, because some power is lost inside the box. Then divide by 40.
1,070 Wh × 0.85 ÷ 40 W = 23 hours
That is the Jackery Explorer 1000 v2. At 8 hours a night, 23 hours is almost three nights.
Estimates. Your devices may use more or less.
Hours by box size
This table uses 40 watts and counts a night as 8 hours.
| Box size | Hours at 40 W | 8-hour nights |
|---|---|---|
| 300 Wh | 6.4 | 0.8 |
| 500 Wh | 11 | 1.3 |
| 1,000 Wh | 21 | 2.7 |
| 2,000 Wh | 43 | 5.3 |
At 40 watts, a 300 watt-hour box does not last one full night. If you also want Wi-Fi or a phone charger on, Find My Power adds them to the math.
What your machine really uses
40 watts is a middle number. Your machine may use much less or much more. It depends on the model, the pressure and the heat.
ResMed, a CPAP maker, has a power sheet for its AirSense 10 AutoSet. It lists 7 watt-hours with the machine by itself, 22 with the humidifier, and 34 with the humidifier and a heated tube. We read those as watt-hours for each hour of use, which is the same as 7, 22 and 34 watts.
ResMed took those numbers at one group of settings, with pressure from 8 to 15. A different pressure or heat setting will give a different number.
The AirSense 10 user guide lists 53 watts as typical and 104 watts at peak. The AirSense 11 user guide lists 56.1 watts as typical and 73.2 at peak. Our tools count 104 watts as a CPAP's peak.
| Setup | Watts | Hours on 1,000 Wh |
|---|---|---|
| AirSense 10, machine by itself (ResMed sheet) | 7 | 121 |
| AirSense 10 with humidifier (ResMed sheet) | 22 | 39 |
| AirSense 10 with humidifier and heated tube (ResMed sheet) | 34 | 25 |
| The number our tools count | 40 | 21 |
| AirSense 10 "typical" (user guide) | 53 | 16 |
The watts come from ResMed. The hours are our math, not ResMed's.
Check your own machine
- Read the label on the power brick and the "technical specifications" page of your manual. The watts on the brick are the most the machine can draw. ResMed lists a 90W brick for the AirSense 10 and a 65W brick for the AirSense 11.
- Know what heat does. ResMed's AirSense 10 guide says to turn the humidifier off when you run on an outside battery, so the battery lasts longer. Ask your equipment supplier before you change how you use your machine.
- Ask about cables. Both ResMed guides list a DC/DC converter as an add-on. Our math is for the machine's own power brick in the wall-style outlet of a box. Your supplier can tell you which cable fits your model.
- Fill in the FDA's power outage booklet for home medical devices. It asks how long your device lasts on battery power and who to call.
- Make a plan. Ready.gov says to talk to your medical provider about a power outage plan for devices that need electricity.
- Charge the box before a storm. At night, plug in only the CPAP.
Pick a box with room to spare
Start with your machine's watts and the nights you want to cover. Then add room, because heat settings can raise the watts.
A box near 1,000 watt-hours covers two nights at 40 watts by our math. A box near 300 watt-hours covers an 8-hour night only if your machine stays at about 30 watts or less. You can compare two boxes side by side or see our picks.
New to these numbers? Read what a watt-hour is and watts vs. watt-hours. We have not measured any CPAP on any box. See how we check each number.
Questions people ask
Will a 300 watt-hour box last one night?
At 40 watts it lasts about 6.4 hours by our math. At 22 watts it lasts about 12 hours. It depends on your machine's watts.
Does a heated humidifier use much more power?
On ResMed's sheet for the AirSense 10 AutoSet, yes. The machine by itself is listed at 7 and the machine with the humidifier at 22. That is about three times as much.
How many nights will a 1,000 watt-hour box last?
About 2.7 nights of 8 hours at 40 watts, by our math. Fewer if your machine uses more.
Can I run Wi-Fi from the same box?
Yes, but every watt shortens the night. A CPAP and a Wi-Fi router come to 55 watts by our count. A 1,000 watt-hour box runs that for about 15 hours. See how to keep Wi-Fi on in a blackout.
Estimates. Your devices may use more or less. As an Amazon Associate I earn from qualifying purchases. Made with AI tools for research and drafting. Samuel Guerra reviews every guide and checks it against the sources linked on this page.