I see there are commercial 'travel' units but is that what people typically use these days?
There are third party battery solutions available, but they are all rather larger than the CPAP units themselves, and come with laptop-sized powerbricks.
I have the ResMed AirMini... and I like it quite a lot. I've had phones that were bigger. (i mean, they were Nokia Communicators... but still) - I use it whenever I sleep in a bed that is not my own. (ResMed says you shouldn't use it as your primary unit. I dunno if that is just "buy more stuff from us" or if there is a real reason, but it's reporting is way worse than the AirSense 10, and sometimes I like the humidifier, and frankly, I'm willing to pay money for a backup) I would like a battery, but between the size and the fact that I haven't slept away from a power outlet for a while, I haven't bothered to buy one.
Is this typical? I don't know. I know a fair number of people who use CPAPs (seriously, if you are overweight, you should probably get it checked out. It's one of the problems modern medical science can actually solve pretty reliably. Makes a big difference.) I'm the only one I know who has a portable cpap. Everyone else I know just carries an extra bag when traveling.
You can often find inexpensive units on Craigslist. I think it's a great investment to have a second set that's always packed and ready to go.