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Short answer: a mid-size 768Wh power station runs a CPAP for about two full nights (16 hours) with the humidifier off, or roughly one night (5 to 7 hours) with a heated humidifier running. The humidifier is the whole story here. A CPAP blower alone draws 30 to 60 watts, but switch on the heated humidifier and heated tube and the draw jumps to 90 to 200 watts, which cuts your runtime to a third or less. Below are real numbers by battery size, the math to check them, and the two accessories that stretch every watt-hour.
What a CPAP Actually Draws
CPAP power consumption depends on pressure settings, altitude, mask leaks, and above all the humidifier. Realistic figures for common machines like the ResMed AirSense 10/11 and the Philips DreamStation:
| Configuration | Typical Draw | Realistic Range |
|---|---|---|
| CPAP only, humidifier off | 40W | 30-60W |
| CPAP + heated humidifier | 120W | 90-200W |
| CPAP + humidifier + heated tube, cold room | 150W | 120-200W |
Notice the multiplier. The heated humidifier does not add a little power, it multiplies your consumption by roughly three. In an outage, turning the humidifier off is the single biggest runtime decision you can make. Most machines also let you use the water chamber unheated as a passover humidifier, which adds some moisture at zero extra watts.
Runtime by Power Station Size: Real Numbers
The formula is simple: usable runtime = battery watt-hours ÷ appliance watts × 0.85. The 0.85 accounts for inverter losses and battery management overhead. Here is what that produces across common capacity classes:
| Battery Size | Example Class | CPAP Only (40W) | With Humidifier (120W) |
|---|---|---|---|
| 256Wh | Compact camping unit | ~5.4 hours | ~1.8 hours |
| 512Wh | Small home backup | ~10.9 hours | ~3.6 hours |
| 768Wh | EcoFlow River 2 Pro class | ~16.3 hours | ~5.4 hours |
| 1,024Wh | 1kWh mid-size | ~21.8 hours | ~7.3 hours |
| 2,048Wh | Large home backup | ~43.5 hours | ~14.5 hours |
| 4,096Wh | Delta Pro 3 class | ~87 hours | ~29 hours |
Check the math on the 768Wh row: 768 ÷ 40 × 0.85 = 16.3 hours. With the humidifier at 120 watts: 768 ÷ 120 × 0.85 = 5.4 hours. If your machine runs at the high end of the range, say 60 watts without humidification, that same battery gives 768 ÷ 60 × 0.85 = 10.9 hours, still comfortably more than one night.
What Size Should You Buy?
Work backward from nights of coverage. One night of sleep is 7 to 8 hours. If you want one guaranteed night with humidification, you need at least 8 × 120 ÷ 0.85 = 1,130Wh, so a 1kWh-class unit is the practical floor. If you can sleep without the humidifier, a 500Wh unit covers a full night with margin, and a 768Wh unit covers two.
For most CPAP users preparing for storm outages, the sweet spot is 512 to 1,024Wh: big enough for a night or two, small enough to carry to the bedroom and recharge from a car or a solar panel during the day. Several solid options live in our roundup of the best power stations under $500.
The EcoFlow River 2 Pro deserves a specific mention for CPAP duty. Its 768Wh LiFePO4 battery is rated for over 3,000 full cycles, it recharges from the wall in about 70 minutes, and it is quiet enough to sit on a nightstand. Check the current price of the EcoFlow River 2 Pro on Amazon.
For multi-day outages, or if you also need to keep a refrigerator and medical devices going, step up to a 2kWh or larger unit with solar input. Our EcoFlow Delta Pro 3 review covers what a 4kWh flagship can realistically carry through a week without grid power.
The DC Converter Trick: 20 to 30 Percent More Runtime
Every table above assumes you plug the CPAP’s regular AC power brick into the power station’s AC outlet. That path converts DC battery power to AC, then the CPAP brick converts it back to DC. Each conversion wastes energy.
A CPAP DC converter cable connects your machine directly to the power station’s 12V DC port, skipping both conversions. In practice this recovers 20 to 30 percent of the losses, and it lets some power stations shut off their AC inverter entirely, which saves another few watts of idle overhead all night. A 768Wh unit that gives 16.3 hours through the AC inverter can deliver roughly 19 to 20 hours through DC.
Make sure the cable matches your machine, since ResMed and Philips use different connectors and voltages. Check the current price of a CPAP DC power converter cable on Amazon.
Practical Outage Playbook for CPAP Users
- Turn the heated humidifier and heated tube off. This alone triples your runtime.
- Use the DC cable if you have one; if not, expect the AC numbers in the table above.
- Lower the tube temperature or use passover humidification if you need some moisture.
- Recharge during the day: a car outlet adds roughly 100Wh per hour of driving, and a 200W solar panel can refill a 768Wh unit in 5 to 6 sunny hours.
- Keep the power station charged to at least 80 percent whenever storms are forecast. LiFePO4 units tolerate sitting at high charge far better than older lithium-ion chemistry.
- Test the whole setup for one real night before you need it. You want to discover connector mismatches now, not at 11 pm in a blackout.
If sleep apnea therapy is medically critical for you, or you also run oxygen concentrators or other equipment, read our deeper guide on backup power for medical devices, which covers redundancy planning and what to tell your utility company.
What About APAP and BiPAP Machines?
Auto-adjusting machines (APAP) draw power in the same range as fixed-pressure CPAPs, since the blower and humidifier hardware is identical; the machine simply varies pressure through the night. Your average draw may actually be slightly lower than a fixed high-pressure setting, because the machine spends part of the night at reduced pressure.
BiPAP and ventilator-class devices are a different story. Their dual pressure levels and stronger blowers push consumption toward 50 to 90 watts without humidification, and 150 to 250 watts with it. If you use BiPAP, size one class up: treat a 1kWh station as your one-night floor without humidification, and a 2kWh unit as the floor with it. Run your own overnight test with the power station’s display before an emergency, because prescription settings change the numbers more on BiPAP than on CPAP.
Travel CPAPs like the ResMed AirMini deserve a mention in the other direction. They draw 20 to 30 watts with no heated humidifier option at all, so even a tiny 256Wh unit delivers a full night: 256 ÷ 25 × 0.85 = 8.7 hours.
A Note on Pure Sine Wave Output
CPAP machines contain sensitive motor controllers and should only run on pure sine wave AC power. Every reputable modern power station produces pure sine wave output, but cheap modified sine wave inverters (common in older car inverters) can cause motor whine, overheating, and premature failure. If you use any inverter not listed in this article’s class of equipment, confirm “pure sine wave” appears in its specifications before plugging in your machine.
FAQ
How many nights will a 1,000Wh power station run my CPAP?
With the humidifier off and a typical 40-watt draw, about 21 hours, which is nearly three 8-hour nights. With a heated humidifier at 120 watts, expect roughly 7 hours, so plan on one night per charge.
Can I run a CPAP off my car battery in an emergency?
Yes, with a proper DC converter cable and ideally with the engine idling periodically. A typical car battery holds around 600Wh but should not be drained below half, so treat it as roughly 300 usable watt-hours, enough for one night without humidification. Never run the engine in an enclosed garage.
Does a higher pressure setting use more power?
Yes, but modestly. Moving from 8 to 16 cmH2O might raise the blower draw from 35 to 55 watts. It matters at the margins, but the humidifier still dominates total consumption.
Will the power station’s display stay accurate as the battery ages?
Runtime estimates drift as cells age. LiFePO4 packs typically retain about 80 percent of original capacity after 3,000 cycles, so a 768Wh unit still delivers roughly 13 hours of humidifier-free CPAP use even years into heavy service. Recheck your real runtime once a year.