It almost sounds as if it was wired incorrectly from the factory.
The coach / house batteries are used for an emergency start situation when the chassis battery won’t allow the engine to turn over. When the Emergency Start button is pressed, it ties the house batteries to the chassis battery for a boost to start the engine.
I have an Outlaw 29H. There is one positive cable that runs from the house batteries to a relay on the firewall. If I press the emergency start button, it trips the relay and allows 12V from the house batteries to flow to my chassis battery.
I would try to trace the wiring from the house batteries to see where they are going. I would think they should not be providing direct power to the engine.
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