RayT, welcome to iRV2.com. We are glad to have you join us here. You are correct in the understanding that the house batteries are not in the circuit for charging when the disconnect is off. Winnebago also did not supply a charging line off the altenator in a lot of these units. You could check with a volt meter with the engine running and when off; you should see a voltage rise if it is connected to altenator. There should be a date stamped into the battery case when it was manufactured. I have see brand new batteries with a bad cell. It is important to keep the cells covered with water so be sure to check them often. GOod luck and let us know what you find.
Mike, RVIA & RVSA Certified Master RV Technician
Amy, Dr. Assistant - Roxie & Mei Ling, four legs each
2000 Gulf Stream Scenic Cruiser 450 hp & 1330# torque
06 Saturn Vue, 06 Chevy Z71 4x4 & 2014 Corvette Z51 M7