I have a long and distinguished history of getting bad information from RV dealers. I doubt what they told you is correct.
If I understand what you are saying you are refering to the relay that connects the chassis batts to the coach batts. On the relay on my 14 Tuscany, when the voltage is above 13+ volts on either system the relay locks up. That is too often for me so I installed a switch so I can disable the connection when I choose.
There are manual disconnect switches for each system also.....
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