Thanks for the extensive response...when I first started reading I wasn't sure I could provide all the requested information...but all of your assumptions were correct!
I think switching to the house battery while out makes good sense, and combinging when charging/plugged into shore power. A silly question: is the starting battery usually bank 1, or does it not matter, configuration wise, if it's 1 or 2? I will need to confirm, but I seem to recall the Catalina literature indicating bank 1 was house, bank 2 was starting. Didn't know if there was a general rule of thumb, and if I'm backward, would indicate re-wiring, etc, by a previous owner.
Thanks again for your post!
Doesn't matter...manufacturers wire boats differently. Actually, I should may dealers wire them differently since batteries are installed at dealer prep.
For Beneteau (my manuf), we dont even have the traditional dial based battery combiner. Instead, Beneteau currently uses a set of 3 twisting knobs. The first is a common negative, the second is engine bank, the second is house bank. Same concept though...various combinations of pegs in the vertical position activate and combine the battery banks.
But the concepts still hold. When charging, combine....when on shorepower, doesn't matter, and isolate your engine bank in order to be able to start the boat in case you run down your house bank too low!