A CPAP draws about 50 watts, which is less than a box fan. That single number is the whole post: it means a mid-sized battery covers a night without drama, and it means the machine you were most worried about is the easiest thing in the house to keep running.
Fifty watts is the figure our generator sizing tool lists for a CPAP, and it's the number every calculation below starts from.
The arithmetic
Battery capacity is measured in watt-hours. Divide it by the watts a device draws and you get hours. Using the capacities from our own reviews:
| Battery capacity | ÷ 50 W | On paper |
|---|---|---|
| 768 Wh | 768 ÷ 50 | about 15 hours |
| 1,024 Wh | 1,024 ÷ 50 | about 20 hours |
| 1,152 Wh | 1,152 ÷ 50 | about 23 hours |
| 2,048 Wh | 2,048 ÷ 50 | about 40 hours |
Plan on less than the table says. Turning battery power into wall power costs something, and the battery's own electronics take a small share. We are not going to hand you a percentage for that, because we could not find one worth citing — just treat the arithmetic as the ceiling, not the estimate.
The thing that actually changes the answer
The humidifier. A CPAP moving air is a small load; a CPAP heating water and warming a hose is a different machine with a much bigger appetite. Some people need the humidification and some genuinely don't, and that's a conversation for the person that prescribed it — but for one night on battery, running the machine dry is the difference between comfortable margin and watching the percentage drop.
Two minutes tonight settles it for your household:
- Find the label on the back or underside of the machine. It lists volts and amps, or watts directly.
- If it lists volts and amps, multiply them. That's your watts.
- Note whether that rating is for the machine alone or with the humidifier running.
- Write the number on a strip of tape and stick it to the power station.
DC or AC
Most power stations offer both a household outlet and a DC output. Many CPAPs can run from DC with the right cord, which skips the step of converting battery power into wall power — and skipping a step generally wastes less. We can't tell you how much less without a measurement we don't have, so treat it as a reason to ask the equipment supplier about a DC cord, not as a number to plan around.
One thing is worth knowing regardless of which output you use: a power station left with an AC outlet switched on is spending power on the inverter itself, whether anything is plugged in or not. Switch the outlet off in the morning rather than leaving it live all day.
Rehearse it once
The whole plan is one cable and one decision, and both are easier to sort out on a quiet Tuesday than at two in the morning.
- Plug the machine into the battery and run it for a night. Nothing is learned from a plan that has never been used.
- Check the battery's remaining percentage in the morning. That's your real number, and it beats every table on this page.
- Note where the cord lives. Taped to the power station is a fine answer; "in a drawer somewhere" isn't.
- Decide in advance whether the humidifier stays on. Making that call while half awake is how a battery gets emptied by breakfast.
Where this falls short
This post is about a small electrical load and a battery. It is not a statement that a battery makes powered medical equipment dependable, and we won't pretend otherwise.
If someone at home relies on a machine to sleep or to breathe, the real plan has three parts and none of them is arithmetic: call the utility and ask to be added to the medical priority restoration list, ask the equipment supplier what they recommend for outages and whether they stock a DC cord for your exact model, and know where you would go if the outage runs long. A battery is a comfortable bridge for a night. It's not a substitute for any of that.
And a battery that has been sitting in a closet since last spring is a battery at an unknown state of charge. Top it up on a schedule you'll actually keep — the first of the month, or whenever the smoke alarms get tested.
Where to go next
The generator sizing tool adds a CPAP to the rest of your list so you can see the whole household load at once. If you want the concept behind why some appliances need far more power to start than to run, surge watts vs running watts covers it — a CPAP is the rare device where the two are the same.