Work out CPAP runtime on a portable power station with simple watt-hour math, humidifier on or off, and a DC option for longer nights.
- Find your machine's real watts with a plug-in meter, not just the label.
- Runtime is battery Wh x 0.85 divided by watts.
- Humidifier off and DC power stretch runtime; confirm choices with your care provider.
A CPAP machine is one of the most reasonable things to put on backup power. It draws very little compared with a kettle or a heater, so a modest battery can cover several nights. The trick is knowing your own machine's draw, because the humidifier changes the answer a lot.
This guide gives you the math, a sample runtime table and a few ways to stretch a battery. It is general information only. Your device, your prescription and your sleep clinic come first, so talk to your care provider about an outage plan.
Step one: find your machine's real wattage
Look at the label on the machine or its power adapter, and check the user manual. Many manuals list average and maximum power use. The label rating is usually a ceiling, not what the machine pulls on a typical night. Pressure setting, mask leaks and humidifier use all change the real number.
- Machine only, no heated humidifier: usually a low draw, often in the tens of watts.
- With a heated humidifier and heated hose: noticeably higher, often several times the machine alone.
- A cheap plug-in watt meter between the wall and the adapter shows your true draw over a night. This is the best way to get a number you can trust.
The runtime formula
Take the battery capacity in watt-hours (Wh), multiply by about 0.85 to allow for inverter losses, then divide by your machine's watts. The result is hours of runtime.
Example: a 500 Wh power station, a machine pulling 40 W. 500 x 0.85 = 425 Wh usable. 425 divided by 40 is about 10 hours. That is one night with a little margin.
Sample runtime table
These are illustrations only. Swap in your own watts.
- 300 Wh battery, 30 W (humidifier off): roughly 8 hours.
- 300 Wh battery, 60 W (humidifier on): roughly 4 hours.
- 500 Wh battery, 30 W: roughly 14 hours, enough for one night plus spare.
- 500 Wh battery, 60 W: roughly 7 hours, about one night.
- 1000 Wh battery, 30 W: roughly 28 hours, two or more nights.
- 1000 Wh battery, 60 W: roughly 14 hours, one night with spare.
Cold weather lowers usable battery capacity, so leave margin if the station sits in a cold room. See power stations in cold weather.
Ways to stretch runtime
- Turn the heated humidifier off, or use it on a lower setting, if your care provider says that is acceptable for you. Some people can use the passive humidity setting or a warmer room instead.
- Use a DC connection if your machine supports it. Many machines can run from a 12 V DC cable, which skips the AC inverter and wastes less energy. Only use the cable made for your model and check the manual first.
- Skip the heated hose if the room is warm enough that condensation is not a problem.
- Keep the rest of the load away. Do not share the station with a TV, lights and phone chargers overnight if runtime is tight. See what to plug in first.
- Recharge during the day from a wall outlet at a friend's place, a vehicle, or solar. See charging with solar panels.
What to look for in a power station
For CPAP use, focus on three things: enough watt-hours for the nights you want to cover, a pure sine wave AC output (the usual spec on current units, but check), and a quiet, low-power standby so the station does not drain itself while idle. The inverter should stay on without auto-shutoff at low loads. Some stations shut off if the draw is very low, so test your setup at home before the next outage. Our power station hub lists options to compare.
Test it before you need it
Do one full practice night on battery. Note how much charge is left in the morning. That single test replaces guesswork and shows whether the humidifier setting, hose and any extra items fit your plan. Keep the station charged, and top it up every few months.
Also write down a backup plan: where you will charge, who to call if the machine fails, and what your provider advises if you must go a night without therapy. For the wider picture see CPAP and medical devices in a power outage.
Quick answers
Can I run a CPAP on a small power bank?
Only if the power bank is made for it and supports your machine's voltage and power. Most phone-size power banks are not suitable. Check your machine's manual and ask your supplier.
Is it safe to skip the humidifier?
Some people can, some cannot. Dryness and discomfort vary, so ask your sleep clinic what is acceptable for you during an outage.
Will the station keep running all night?
It should, if capacity covers your hours and the inverter does not auto-shut off at low load. Test a full night at home.