After putting my maintaining charger on the third battery the battery cranking bank was dead. Pushed boost switch and no help. House batteries seem to be charged.
Put battery charger on cranking bank and started with ease. This boost switch has some sort of issue. Have appointment at MOT on 19th to fix front a.c. and look at boost switch.
I inspected a coach that the owner claimed was always hooked up, he'd had the same problems with starting. Fired the boost, NADA. He had no in-coach type of battery indicator that showed both engine & coach charge. The dweeb charger he bought did work upon starting, but not again. I talked him in to buying all fresh batteries, both sides. YES!
I had a similar problem with my boost switch - it would not connect the two battery banks. I checked the isolator panel and relays and decided to change out the relays due to corrosion (what else...). I also cleaned all the connections and replaced the grounding cord. That fixed the boost switch and as a bonus fixed issues I had with the dash air switches. The panel on my coach is located under the bed on the forward pedestal bulkhead (closest to front, opposite breaker box).