About the altitude, I don't know and will leave that to others.
It's good that you're starting your research early. A few months should be enough, assuming that your budget allows some major spending between now and your trip. You say that you've read previous discussion threads, but there are a lot of them and possibly you've missed a few? I don't think they're all very old, but maybe I'm remembering wrong. Anyroad, I suggest searching for thread-title (page-title) keywords "camping" or battery" or "batteries" or "canoe". Of course you can skip all the stuff about using UPS configurations at home.
Here is sort of a random brain dump of things that occur to me at the moment. FYI, FWIW, HTH, etc. I hope others will chime in to fill in details that I don't know or didn't think to mention.
Folks who do a lot of car or motorcycle or RV traveling often suggest using the regular old CPAP machine that you use at home, with the humidifier heater switched off and no heated hose. However, although that's a good idea for use in and around motor vehicles, I don't think it's all that appropriate for backpacking. My travel-machine choice so far, and I'm within a few months of buying one but have no experience with it yet, is the Dreamstation Go, despite the fact that I much prefer Resmed's algorithms for APAP and everything else. However, my reasons aren't anybody else's reasons, so in your case it's good to also consider the Resmed Airmini and possibly the Somnetics Transcend (although that one is somewhat of a dark horse, not popular and rarely mentioned). The Airmini needs a smartphone to configure it; the DS Go doesn't. The Airmini can be used only with a few specific Resmed masks; the DS Go should be usable with any mask as far as I know. The Resmed masks are "P10 for Airmini" (a special edition of the P10), the N20, and the F20. At least the N20, and possibly the F20, needs a converting connector to use it with the Airmini. So each of those masks should be available in a special package labeled "for Airmini".
The HDM Z1 is not recommended at all, quite the opposite, for a lot of reasons I won't go into here. If you're wondering why, you could read the reviews & discussions about the thing, but IMAO that would be a waste of time that you could much better spend on learning about the DS Go and the Airmini and maybe the Transcend. (If you do search apneaboard for "hdm" or "z1", I think you'll need to use an outside search engine, if apneaboard's local search facility still has the misfeature of rejecting search terms shorter than 4 characters.)
Batteries are a huge problem. This is probably a stupid question, but can you recharge lithium-ion batteries during your trip? If not, then you're kind of out of luck in some ways and you might have to forgo the CPAP after a night or two or three, unless you can somehow carry many, many pounds: many high-capacity battery packs charged just before you leave and used to depletion (which probably isn't good for 'em) one at a time. Or, alternatively, a heavy battery of a type other than Li-ion, with a much higher capacity. And using that to depletion certainly isn't good for it either. Details are in those various past discussion threads.
Philips sells a battery for the DS Go (by the way, that machine takes 24V, not 12V as the full-size Dreamstation does), but it retails for $300, which is a huge ripoff. I posted a review of a Gissaral 12V product, 130 watt-hours, in the "Other Product Reviews" forum a while back, and that'll give you some idea of what you're up against. It gets rather grisly, definitely TMI territory:
http://www.apneaboard.com/forums/Thread-...power-bank
That one wouldn't be my first choice (I bought it partly because it's cheap); at the moment, without having bought one of these yet, I'm leaning toward the Renogy RC-P72000, which is 266 watt-hours for about $160. Another good one is the XTPower MP-50000, 195 Wh, $200. As you can see, if you'll need to carry several of any of those for many nights of CPAP use, it gets very expensive. So it helps if you're obscenely rich.
With any third-party battery, you need to kluge together your own power cable. For the DS Go, that has to be in addition to a 12V-to-24V converter, assuming that you're not using one or more of the expensive Philips 24V batteries. I can't remember what the capacity (in watt-hours) of the Philips battery is, but I think it's quite low, probably only enough for one night of CPAP use. For the DS Go, the DC-DC converter that I suggest is the Bixpower model DD90M-24V, available on Amazon, very small and lightweight, high efficiency (supposedly 96%), about $50.
When you're shopping around, battery capacities that are expressed in milliamp-hours can be converted to watt-hours by multiplying by 3.7/1000, because 3.7V is what a fully charged lithium-ion cell puts out. Using that Renogy model as an example, its description says 72000 mAh (72 Ah), and multiplying 72 by 3.7 gives 266 Wh. It's best to convert everything to watt-hours before comparing products.
A battery that is sold specifically for CPAP use will, if it's intended for only one night's use, typically have a capacity somewhere around 96 Wh: assuming 1 amp of current draw (no humidifier or heated hose!) and 8 hours at 12 volts, that's 1 times 8 times 12 = 96 watt-hours. 1 amp is, for some machines, an over-estimate. Examples of those lithium-ion batteries sold for CPAP use are: BPS Freedom, 97 Wh; Medistrom Pilot 12 or Pilot 24, 98 Wh; Philips "PAP Battery Kit", 90 Wh; Resmed "Power Station II", 97 Wh. Again, only one night each before recharging! The Philips and especially the Resmed products are outrageously, ridiculously expensive, around $500 and $700 respectively. To be avoided. The others are less expensive but still not really affordable compared to the many random third-party Li-ion batteries easily available and usable with some cable kluging. Just be sure to get the polarity right before connecting anything. (Oops!)
If you take your Resmed A10 on the trip instead of buying a travel CPAP machine, you'll need either the Resmed DC-to-DC converter (part 37297) or the similar but better Battery Power Solutions product: Amazon search string "battery power solutions 24v power converter for air 10/s9 series". The Resmed converter has, unfortunately, a cigar-lighter plug as the input power connector, but the BPS is more versatile and has a more usual 5.5x2.5mm or 5.5x2.1mm (can't remember which) co-axial plug that will fit some 3rd-party battery packs. There are 5.5x2.1mm to 5.5x2.5mm adapter cables and connectors also easily available. Those two DC-to-DC converters are specifically for the Resmed A10 and S9 machines; they provide the Resmed secret Masonic handshake, which most other DC-to-DC converters don't. Without that secret handshake, the A10 no workee.
It's obviously much easier to use, for instance, a DS Go with its own Philips battery, but that's super-expensive and you don't get the extended capacity (more than one night) of the 3rd-party batteries like Renogy, XTPower, etc. The best (because least hassleful) solution if money is no object is a DS Go, your favorite mask, and a backpackload of charged-up Philips expensive proprietary DS Go 24V battery packs with no additional custom cable or converter needed.
When I get a DS Go I'll figure out the DC connections and kluge together a cable for one of those less expensive & higher capacity 3rd-party batteries, but that won't be for some months, so good luck and have fun, whichever conglomeration of products you decide on. It's certainly an adventure ... long before you reach the trailhead! It helps if you're really into electronic gadgets & power supplies. If not, it might be good to enlist the help of a friend who is. That's assuming that you can't just throw a lot of money at the problem and call that George.
