Electrical problem..Magnatec converter?

Sometimes, problems like these are difficult to explain. This same scenario occurred once before, while in the storage building. I charged the house batteries-2 12v deep cycles newer batteries, and didn't have any more problem for months until now. The fact that the house and engine batteries were 'dead', is confusing. There are, as I recall, 3 separate solenoids 'under the hood' so I'm guessing normally the converter/charger is hooked up through all 3 batteries. Next, I'm not sure if the charger function of the converter feeds off of the 'Recep' breaker, or if its hot wired directly to the shore power connecter....if that's clear. With only the 'main' breaker on, I can't hear any hum or anything directly at the converter. Normally, when it warms up, the converter fan cuts on and you hear it. If one of the house batteries was bad, the system would probably never work properly. I may need to pull them out and have them load tested. I'm guessing possibly the engine battery could have gone bad which might suck the house batteries 'dry' since all 3 'died' in a matter of a few days. There was no known power draw. Fridge off, no lights,WH is propane. I would not have thought the house batteries would in way connect to, or through the engine battery. Hope my rambling has some clarity. I do appreciate the help guys, eventually I(or, we)will figure this out. Sadly, apparently there is no wiring diagram of the coach.