Ditto on the dead battery trying to draw more than 30 amps. Get it charged back up if it will take a charge. That is severely low.
Your alternator should be charging it but it seems that circuit is not working for you. Start the engine and press the emergency start/aux start button. Prop it in the active mode or have someone hold it down. Then measure the voltage on the dead battery.
If the previous test does not show the second coach batteries getting charged then start looking for a blow fuse. It could be the combining solenoid but that can be chased later.
