I have the Resmed Astral 150 and am very happy with it. I highly recommend it to anyone getting a "bipap" (non invasive ventilation device). I use it between 10 and 16 hours a day. I can no longer lie flat without using the Astral 150.
The Astral 150 has an internal battery that is rated for about 6 hours of operation. I also have two external Resmed batteries that are good for another 8 hours each. That comfortably gives me over 20 hours of use, which is a great comfort living in a place where we occasionally get power outages.
It also makes it very convenient for taking longer trips.
The Astral 150 can also work off of 12 volts, such as found in a car or single wheelchair lead acid battery. It requires a separate adapter to do this, and I found a new, original resmed adapter on ebay.
When my wheelchair batteries are at end of life for wheelchair use, they actually have a lot of life left in them for other purposes, such as powering the Astral 150. I always keep a pair of these old wheelchair batteries and have then connected to a maintenance charger. This assures me that I have many hours of battery power available for the Astral 150.
We also have a small, portable, gas-powered generator. If power goes out for longer than I am willing to rely on batteries, we could always fire up the generator.
We have thoroughly tested all of this with the Astral 150 and have found that this setup works very well.
Steve