You're last post mentions the engine batteries. My post referred to the coach batteries.
Also, you did not post how you know the boost button provides no boost. It is important to understand why you feel there is a problem.
VDC = Voltage Direct Current You'll need a volt/ohm meter to take the readings.
The boost button connects the coach and chassis batteries. One must keep the button depressed for it to work. When released the connection between the chassis and coach batteries is broken. The boost button is meant to provide this connection only for short periods of time. The boost button is there to provide extra engine starting power, if needed.
2005 Newmar KSDP 3910 + GMC ENVOY XUV 37K lbs Moving Down The Road
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