Kinda depends on what equipment you are using and whether or not you require humidifier/hose heater.
I'm using Philips Dream Station that is 12v, so a simple cig lighter adapter cord gets you started. I am also looking into smaller travel solutions, but my machine is pretty specialized and there are no travel sized units!
For motorcycle rides, I have a 9Ah LIFEPO battery that will get me 2-7.5+ hour nights without humidifier and I have cords to recharge it enroute through my battery tender plugin.
For Jeep rides, I'm usualy towing my Tentrax that has an onboard battery with a cig lighter inside.....Easy.
Lots of options if you are creative and have the right equipment
I run a goal zero yeti 400 and it lasts about 8 hours with everything running, humidifier on. I also have the goal zero solar panel briefcase so I can charge the battery during the day.
Ya, that humidifier draws serious power! My air pump draws about .5Ah, but humidifier draws about 5.5Ah!
This last 2 week trip in the desert, I was starting to have an issue with my nose drying out from not using humidifier, but I suppose I could have taken the attachment for and not turned it on for some passive humidification. Figured taking distilled water was just something else to pack.
Currently thinking about setting up the JTR for solo overlanding trips. But for dry camping in the RV, I use a sealed 12v battery with my older cpap machine I keep in it. I do not use the humidifier. I can last almost a full week.
My plan on the Gladiator is to use a smaller motorcycle battery ( I already have one for shorter trips in the RV ), and charge it while on the go with my small B&D battery charger/maintainer plugged into the rear outlet in the bed.
I haven't tried it yet, it's just an idea at this point!