Your experience is very similar to mine. House batteries would not charge until I hit the boost button. Then they would behave normally. I have an ‘04 Imperial which has an Intellec IRD. The IRD sends a signal when the chassis batteries have reached 13 volts or so, indicating that the alternator has pretty much charged them and it can handle the high current from the additional house batteries. When I investigated my system, I found that the signal to the IRD was always lower than the chassis batteries, causing the IRD to not tell the IRD to connect. It seems that the place the IRD got the chassis voltage was being reduced by loads on that line. My solution was to add another relay which connected the IRD to a solid voltage source. I did this in 2009 and have not had any problem with house batteries being charged since.
i don’t know if you have an IRD or not. The Intellec IRD is located on that big fuse panel located in the driver side outside area. Another indication will be that you have a Lambert LE 415 to charge the chassis batteries from shore or genset power.
it looks that the files from the old Monacoers group was lost with the new group, but I did a write up which was there.
Dick L ‘04 Imperial