<span class="highlight">CPAP</span> [ Sleep apnea machine ]

I went through this some years ago and I found most at that time used a 240 to 12V DC power supply although it was not alway obvious straight away.

Some of them supplied a 12V kit consisting of a simple ciggy to DC plug and charged very high prices whereas you can make a lead or by on eBay for only a few dollars.

I have Resmed machine with a humidifier when brought I paid for a 12 volt adaptor .What they draw I don't know but turn the humidifier off and you should have no probs

Just check the specs.
I helped out a bloke who had one to find his battery was flat after 6 hours.
Detailed look at the specs showed 5 amp draw at 12 volts

As has been said find a machine that can run direct on 12v without the need for expensive 12v adapters.
I have two machines one at home and one in the Oka and both run direct on 12v. One is a Phillips Respironics and one a Devilbiss Intellipap II that has a lower power draw than many others even with the humidifier running.
Steer clear of Resmed machines as they run on 24v and require an expensive power cord for 12v use as well as a penalty for the extra power usage caused by the power supply having to step up from 12v to 24v for the machine.
My experience with the so called travel machines is that while they usually lighter with a smaller footprint they are often much noisier than a full size machine and possibly not as long lived or robust.
As I use a nasal pillow because I have a beard I find that humidifier use is necessary to avoid the air drying my nasal passages out.
We have a large lithium battery and plenty of solar so power use isn't a problem for us.
I have taken my Devilbiss machine on a touring trip sleeping in a swag and it was fine with a 12v lead running from the tour mob's catering trailer overnight.

I have a Resmed S10, and it uses 4-5A at my settings (heated tube and humidifier) with the 12v power converter..

I found out the hard way last sept that my old boy’s 24v unit running through the inverter will happily flatten my 3 x 120a battery setup in the camper each night.
Moral = buy the right one.

Yeah , I had my brother sharing my camper trailer on a fishing trip ,. He had it going all night , I crimped his intake hose off for fun . woke up pretty quick .But ,

Depending on why you need a CPAP a dentist might be able to supply a solution that does not require power.

Look at ResMed Airmini. They are designed for travelling and are pocket sized. They use very little power if you buy the 12-24 volt plug in converter. Don't use a 12-240V inverter as they are known to blow the device up plus it will consume more battery power. It runs on 24V with the converter.
Fully automatic and/or resettable for any need. Cpap or constant modes.
The ResMed site has the details.