So I have been using a CPAP for 13 years and I usually use it one or two times/year on planes, usually long haul.

I used to dutifully call UA to notify about my machine, but then one time I did it for a domestic flight where I thought I *might* use it (the flight was going to get in very late, so I thought I might nap). I think this was maybe 6 years ago and United had changed their process where if I called about the CPAP, then it did something to my record where I could no longer check-in online, even though the counter agents never asked about the CPAP when I went to the counter (except one time where an outstation Express agent questioned me about it and had no clue what she was talking about). Anyway, on this particular flight I had a misconnect and spent the night at some airport hotel and the next morning when I was trying to improve the flight I was rebooked on since other inventory had opened up, I couldn't do anything myself because of the stupid notation that I had a CPAP on my reservation (which I didn't even end up using during the intended flight because of the misconnect). I eventually got through to an agent (and I think I lost out on one flight in the intervening time) and I had them remove the note on my record so I could actually work with it and I eventually was able to get on a different flight, but it was a lot of unnecessary hold time and frustration.

Since then, I never call UA. I travel with one of two CPAP machines depending on the length of trip and I already know they are both (Resmed S8 and AirMini) on the approved list. I also don't have external batteries; I just plug them into the onboard power. And no one on United ever says a word. Would I say you do this if you are just starting out (i.e. have never checked that your machine is ok on UA) or on other airlines, no. But for me, on United, this works just fine.

If I'm traveling with the S8 (which means I'm on a longer trip and want water-based humidification, and I only use tap water when traveling), I use my original CPAP bag as it is a decent/right size. I haven't had anyone complain about too many carryons in awhile since on a longer trip, I've checked a bag. If I'm using the AirMini, that is packed in (2) 1-quart bags for the various parts, then those 2 bags go in a small packing cube to keep them together, and then that goes in my backpack. And I pack a one-foot, three-prong, three-outlet power strip as that generally seats better in the airline's power and it gives me an extra outlet if I want to charge my phone or something. Plus, the brick on the AirMini is a little unwieldily compared to a normal plug.