With the humidifier and heated tube switched off, a CPAP at a typical 8 to 10 cm H2O runs about one night (8 hours) for every 100 watt-hours of battery. ResMed's published figures put a dry AirSense 10 at 9.5 to 11.2 watts at those pressures. Switch the humidifier on and the draw rises 2.5 to 6.7 times, so the same battery lasts hours, not nights.
How many watts does a CPAP actually use?#
Far fewer than circulating figures suggest, and far more once you add heat. ResMed's technical services battery guide lists the current each of its machines draws from a 12 volt battery, pressure by pressure. For the AirSense 10 range (CPAP, Elite, AutoSet and AutoSet for Her) running from a battery through ResMed's DC/DC converter, multiplying by 12 V gives watts and multiplying by 8 hours gives a night:
| Pressure | Dry, SlimLine tube | Humidifier on 4 | Humidifier on 8 | Humidifier on 8 plus ClimateLineAir tube at 30 degrees C |
|---|---|---|---|---|
| 6 cm H2O | 0.70 A, 8.4 W, 67 Wh | 1.73 A, 20.8 W, 166 Wh | 3.44 A, 41.3 W, 330 Wh | 4.71 A, 56.5 W, 452 Wh |
| 8 cm H2O | 0.79 A, 9.5 W, 76 Wh | 2.00 A, 24.0 W, 192 Wh | 3.49 A, 41.9 W, 335 Wh | 4.77 A, 57.2 W, 458 Wh |
| 10 cm H2O | 0.93 A, 11.2 W, 89 Wh | 2.30 A, 27.6 W, 221 Wh | 3.66 A, 43.9 W, 351 Wh | 4.92 A, 59.0 W, 472 Wh |
| 12 cm H2O | 1.06 A, 12.7 W, 102 Wh | 2.61 A, 31.3 W, 251 Wh | 3.86 A, 46.3 W, 371 Wh | 5.12 A, 61.4 W, 492 Wh |
| 16 cm H2O | 1.23 A, 14.8 W, 118 Wh | 3.33 A, 40.0 W, 320 Wh | 4.18 A, 50.2 W, 401 Wh | 5.37 A, 64.4 W, 516 Wh |
| 20 cm H2O | 1.66 A, 19.9 W, 159 Wh | 4.19 A, 50.3 W, 402 Wh | 4.59 A, 55.1 W, 441 Wh | 5.61 A, 67.3 W, 539 Wh |
Pressure matters, but modestly: going from 6 to 20 cm H2O a little more than doubles a dry machine's draw. Heat matters enormously: at 10 cm H2O the fully heated setup draws 5.3 times the dry one, and at 6 cm H2O 6.7 times.
The newer AirSense 11 has no per-pressure table in any document fetched for this page. Its user guide gives a typical power consumption of 56.1 W and a peak of 73.2 W from the 65 W mains supply, without stating the settings. That typical figure sits in the same band as the heated AirSense 10 rows above, which is consistent with it describing a humidified machine, but ResMed does not say so. Until it publishes a dry figure, the AirSense 10 column is the best planning proxy for an AirSense 11 with its humidifier off.
Why two answers circulate#
Search for CPAP battery life and two figures turn up. One says a CPAP needs 120 to 240 watts, which would mean a car battery for a single night. The other says any 15,000 mAh power bank runs a CPAP for 8 to 12 hours. Neither survives the manufacturer's numbers.
The high figure confuses the rating of the power supply, or of the inverter a camper might buy, with what the machine draws. ResMed's own guide measures a heated AirSense 10 at no more than 67.3 W even at 20 cm H2O with everything turned up.
The low figure ignores the unit conversion and the humidifier. A 15,000 mAh bank is rated at the 3.7 volt cell level, so it holds 55.5 Wh, and at the 85 percent delivery figure we use in power bank sizing it delivers about 47 Wh. At 8 cm H2O, dry, that is about 5 hours, not 8 to 12. It is also only possible if the bank has an output the CPAP can use: the machines here run on 24 V, through a mains supply, a vehicle DC converter or a dedicated CPAP battery cable, not from a USB port.
How long will a battery last? Four sizes compared#
To turn watts into nights you need the energy a battery actually delivers, which is less than the label. We use the same assumptions as the rest of the site: lithium-ion packs and power stations deliver about 85 percent of their rated watt-hours through their own electronics; a 12 volt battery feeding ResMed's converter directly is limited by how deeply it can be discharged (ResMed's current figures are measured at the battery, so the converter loss is already in them).
| Battery | Energy you can plan on | Dry | Humidifier on 4 | Humidifier on 8 | Humidifier on 8 plus heated tube |
|---|---|---|---|---|---|
| 95 Wh CPAP lithium pack | about 81 Wh (85 percent) | 7.2 h, 0.9 nights | 2.9 h | 1.8 h | 1.4 h |
| 500 Wh power station, 12 V DC socket | about 425 Wh (85 percent) | 38 h, 4.8 nights | 15 h, 1.9 nights | 9.7 h, 1.2 nights | 7.2 h, 0.9 nights |
| 100 Ah AGM or lead-acid deep-cycle | about 600 Wh (50 percent) | 54 h, 6.7 nights | 22 h, 2.7 nights | 14 h, 1.7 nights | 10 h, 1.3 nights |
| 100 Ah lithium iron phosphate | about 1,024 Wh (80 percent) | 92 h, 11.5 nights | 37 h, 4.6 nights | 23 h, 2.9 nights | 17 h, 2.2 nights |
The rule that falls out: dry, about one night per 100 Wh you can actually use; heated, about one night per 500. At 6 cm H2O dry, the per-night figure falls to 67 Wh; at 16 cm H2O it is 118 Wh, so scale the table by your own pressure from the first table.
The 95 Wh pack, checked against its maker. Medistrom described its 95 Wh Pilot-24 Lite as giving "approximately 1-2 nights" at an average pressure with humidifier and heated tubing disabled. Against ResMed's AirSense 10 figures, one night holds up to about 10 cm H2O; a second night would need under 5 W average, below what ResMed lists for that machine even at 6 cm H2O. Two nights is realistic only for a machine that draws much less. ResMed's AirMini, a travel CPAP, lists a typical consumption of 6.3 W, which would give about 13 hours from the same 81 Wh, if that typical figure matches your settings.
The deep-cycle figures, and why lithium is ahead. ResMed's guide says true deep-cycle batteries can be discharged "as much as 80% or more", and most marine batteries "up to 60%". We plan lead-acid at 50 percent because going deeper shortens its life, as covered in 12 volt power and fridges. Battle Born rates its 100 Ah lithium iron phosphate battery at 100 percent usable depth of discharge and calls it equivalent to 200 Ah of lead-acid; the table keeps the more conservative 80 percent.
Can you run a CPAP off a car battery?#
You can, and both ResMed and Philips supply cables to do it, but a starting battery is the wrong battery. ResMed's guide says automotive batteries "should never be discharged by more than about 30% before recharge" and that a car battery "will only last about 30 deep cycles". For an example 60 Ah starter battery, 30 percent is 216 Wh, about two dry nights at 10 cm H2O, and each one costs some of the battery's life and leaves less to start the engine.
Two warnings are in both makers' documents:
- Do not start the engine while the CPAP is connected. ResMed: "dangerous voltage spikes are produced that can damage the unit." Philips: the device "should not be used while the vehicle's engine is running."
- Use the maker's own DC cable or converter. ResMed's converter shuts off when a 12 volt battery falls to 10.5 V, which protects the battery from a full discharge and you from a dead car. Philips says to use only its DC power cord and battery adapter cable.
A separate auxiliary battery charged from the vehicle, as described for fridges in 12 volt power and fridges, solves both problems: the CPAP never touches the starting circuit.
Inverter or DC converter?#
Use DC whenever you can. A power station's mains socket runs an inverter that turns 12 V into mains voltage, and the CPAP's own power supply then turns it back to 24 V.
ResMed measured the same machines both ways. For its S8 Lightweight and S8 Escape, at the same pressures:
| Pressure | Through an inverter | Through the ResMed converter | Extra draw from the inverter route |
|---|---|---|---|
| 6 cm H2O | 1.02 A | 0.80 A | 0.22 A, 27 percent |
| 10 cm H2O | 1.24 A | 1.02 A | 0.22 A, 22 percent |
| 16 cm H2O | 1.62 A | 1.37 A | 0.25 A, 18 percent |
| 20 cm H2O | 1.90 A | 1.66 A | 0.24 A, 14 percent |
For the S8 Elite and AutoSet group the extra was 0.23 to 0.39 A, 23 to 30 percent. The pattern matters more than the model: the inverter adds a roughly fixed 3 to 5 watts, a large share of a dry CPAP's 8 to 12 W and a small share of a heated one's 60. For an AirSense 11 the DC route is the Air11 DC/DC converter listed in its user guide; for an AirSense 10, the Air10 converter named in the battery guide.
Do you have to turn off the humidifier?#
On some setups you have no choice. Philips's DreamStation 2 manual is explicit: with its battery pack attached the machine shows "Humidifier Off" because "the attached battery does not support humidification", and "an 80W power supply is required to support humidification". ResMed's guide adds, for its S9 humidifier, that the figures "will vary dependant upon relative humidity", so treat the humidified rows as a guide rather than a promise.
Running without humidification is a therapy decision as well as a battery one. If dry nose or mouth is a problem for you at home, ask your clinician before a trip how to manage a few nights without it. On the power side, the halfway settings help: at 10 cm H2O, humidifier on 4 without a heated tube draws 27.6 W against 59.0 W fully heated, which turns a 100 Ah lithium battery from about 2 nights into about 4.6.
The limits: cold, altitude and charging#
The battery arithmetic stops applying outside the machine's own operating range, which is narrower than most campers expect.
| Machine | Operating temperature | Operating altitude | Power |
|---|---|---|---|
| ResMed AirSense 11 | 5 to 35 degrees C (41 to 95 degrees F) | sea level to 3,010 m (9,870 ft) | 65 W supply; typical 56.1 W, peak 73.2 W |
| ResMed AirMini | 5 to 35 degrees C (41 to 95 degrees F) | sea level to 2,591 m (8,500 ft) | typical 6.3 W, peak 27 W, standby 1 W |
| Philips DreamStation 2 | 5 to 35 degrees C (41 to 95 degrees F) | 0 to 2,286 m (7,500 ft) | 80 W supply needed for humidification |
- Cold. All three stop their operating range at 5 degrees C. A tent on a frosty night can fall below that, so on a cold trip sleep where the air stays above 5 degrees C, such as inside a vehicle, rather than relying on the machine to cope. A cold battery also delivers less, and a lithium battery must not be charged below 0 degrees C (the charging limits).
- Altitude. The three ceilings run from 2,286 m to 3,010 m, a spread of more than 700 m between machines. Check your campsite's elevation against your own machine's figure, not against another model's.
Measure your own night before you trust the table#
- Find your pressure. ResMed sized its own tables on the 95th percentile pressure for automatic machines, not the average, so use that figure from your therapy data or ask your clinician for it.
- Fit a DC power meter. An inline watt-hour meter between battery and converter (or a power station's own output display) records what the night actually used.
- Run one full night at home with exactly the settings you will use at camp: humidifier off or on the level you plan, heated tube off or on.
- Read the watt-hours in the morning and divide your battery's usable energy (from the second table) by that figure. Plan on 80 percent of the answer to leave margin for a cold night or a bad seal.
- Add your other loads. Phone, headlamp and fan go in the power budget calculator alongside the CPAP figure.
For trips longer than the battery, recharge comes from driving with a DC to DC charger or from a panel; the harvest figures are in solar for camping.
Common mistakes#
Leaving the heated tube on. At 10 cm H2O the heated tube and humidifier on 8 add about 48 W to an 11 W machine. It is the single setting that turns a five-night battery into a one-night battery.
Running through the power station's AC socket. The inverter route costs 14 to 30 percent more on ResMed's own measurements. Use the 12 volt socket and the maker's DC converter.
Draining the car's starting battery. Thirty percent is ResMed's limit for an automotive battery, and starting the engine with the CPAP connected can damage it.
Packing the CPAP battery in checked luggage. Spare lithium batteries fly in the cabin, under the 100 Wh and 160 Wh limits set out in power banks on a plane. A 95 Wh pack is under the lower limit.
Frequently asked questions#
How many watts does a CPAP machine use?#
With no humidifier or heated tube, about 8 to 20 watts: ResMed measures its AirSense 10 at 8.4 W at 6 cm H2O and 19.9 W at 20 cm H2O from a 12 volt battery. With the humidifier on its highest setting and a heated tube at 30 degrees C, 56 to 67 W. The AirSense 11 manual lists 56.1 W typical and 73.2 W peak.
How long will a 100Ah battery run a CPAP?#
At 10 cm H2O with no humidifier, about 11 nights from a 100 Ah lithium iron phosphate battery planned at 80 percent depth of discharge, and about 6 or 7 nights from a lead-acid deep-cycle battery used to 50 percent. With humidifier on 8 and a heated tube, about 2 nights from lithium and just over 1 from lead-acid.
Can I use my CPAP without the humidifier on battery?#
Yes, and it is the setting that makes battery camping practical: a dry AirSense 10 draws 11.2 W at 10 cm H2O against 59.0 W fully heated. Some machines decide for you: the DreamStation 2 turns its humidifier off when running from its battery pack. If you rely on humidification at home, ask your clinician how to manage a few nights without it.
Can I run a CPAP from a portable power station?#
Yes. Use its 12 volt DC socket with the CPAP maker's DC converter or cable rather than the mains outlet, because ResMed measured 14 to 30 percent more draw through an inverter. A station delivering about 425 Wh runs a dry AirSense 10 at 10 cm H2O for about four nights, and a fully heated one for less than one.
Can I use my CPAP in a tent in cold weather?#
Not below 5 degrees C (41 degrees F), the lower operating limit for the ResMed AirSense 11, AirMini and Philips DreamStation 2. On a cold night, sleep where the air stays above that, such as inside a vehicle, and never charge a lithium battery below 0 degrees C.
What size battery do I need to run a CPAP for a weekend?#
For two nights dry at 8 to 10 cm H2O, plan on about 150 to 180 Wh of usable energy, which means a power station of about 250 Wh rated or a small lithium battery. With the humidifier on 4, plan on about 450 Wh usable; fully heated, close to 950 Wh. Measure one night at home to confirm.
Standards, sources and further reading
- ResMed Technical Services, *Battery guide*, document 198103/4, 2015-08. Current draw at 12 V DC by treatment pressure for each device, with and without humidifier and heated tubing, through a ResMed converter or an inverter; battery size for 8 hours with a 50 percent safety margin; 95th percentile pressure used for AutoSet devices; discharge guidance for automotive, deep-cycle and marine batteries; converter cut-off at 10.5 V.
- ResMed, *AirSense 11 user guide*, Americas edition. 65 W power supply (24 V, 2.71 A); typical power consumption 56.1 W, peak 73.2 W; operating temperature 5 to 35 degrees C; operating altitude sea level to 3,010 m; Air11 DC/DC converter listed as an accessory.
- ResMed, *AirMini user guide*, Asia Pacific edition. Typical power consumption 6.3 W, peak 27 W, standby 1 W; operating temperature 5 to 35 degrees C; operating altitude sea level to 2,591 m.
- Philips Respironics, *DreamStation 2 CPAP user manual*, as hosted by MedCare. "The attached battery does not support humidification"; an 80 W power supply is required for humidification; DC power cord and battery adapter cable for a 12 VDC battery; do not use while the vehicle engine is running; operating temperature 5 to 35 degrees C; altitude 0 to 2,286 m.
- Medistrom Pilot-24 Lite, *product listing*, CPAP Outlet. 95 Wh lithium-ion, 24 V DC output; "approximately 1-2 nights of continuous run-time on average pressure setting with the humidifier and heated tubing disabled". The retailer EasyBreathe lists it as discontinued.
- Battle Born Batteries, *100Ah 12V LiFePO4 deep cycle battery (BB10012)*. Usable depth of discharge 100 percent, lead-acid equivalent 200 Ah, weight 31 lb.
How this page is made. Every number here is either a published standard, a physical constant, or arithmetic we show in full so you can check it. Read our evaluation method and editorial standards, or tell us we got something wrong.
Last reviewed and updated 22 October 2026.