In our 2009 Jayco Greyhawk Class C, the battery disconnect turned everything off except the converter. I learned that the hard way when I replaced the converter. Fortunately, it was just a shower of sparks with no injury.
The CO and Propane detector ran off the house battery and the ignition side of the chassis battery. Which was a nice reminder to disconnect the battery when putting the MH in storage. Whenever the detectors lost power, they would give a little chirp. If I didn't hear the chirp when turning off the ignition, I knew I forgot to disconnect the battery.
-Michael