(06-18-2015, 08:58 PM)GWild Wrote: A 12V 18AH sealed lead battery is about $35. If your xPAP is 12V, and you have the 12V car adapter and mating plug for it, a clip to DC outlet cable and the battery are all you need. A common part number for this type of battery is UB12180 (12V18.0AH)... I saw a 35AH version for $85... but you don't need that much, but it would last longer.
You can run overnight on the $35 battery then recharge it with jumper cables while the engine idles along ... recharge will take 15 to 30 minutes on a healthy alternator.
I have a similar sized battery and it works quite well. The caveat is I paid more for my battery, and it is designed for deep cycle use. While the $35 battery is AGM, they are generally used for starting applications, but it'll probably last several camping trips used this way (think of it as a disposable multi-use battery). So if you have the DC cable to fit your xPAP, and can find the battery and the clip on DC outlet, you should be good to go. Just be sure to fully charge the battery before you leave home. You'd hate to wake up that first night to a new but dead battery.
The OP has an S9 which runs on 24 V DC; and it has a 3 prong DC plug.
Running from DC requires the 12 V DC to 24 V DC converter from ResMed. It get the Voltage to 24 and it provides the 3 prong DC plug.
That route adds about $100 just for their converter. I personally have one to operate on battery in the event of power loss.
I keep a 35 A-Hr scooter battery on a battery tender should I lose power here.