Agree, if properly wired......
After having my boat for two years I could not understand why one bank of batteries would show a charge of 14+v and the other 12+v when hooked up to shore power. I would use the battery selecter switch to check the voltage. To play it safe I decided to just leave the selecter switch on both. Well, I finally looked into it this past weekend....the dealer when installing a combiner (combines both batteries bank when charging, but seperates them when not)forgot to attach the ground. Thus, the solenoid never kicked in whencharging the batteries (and thus always keeping the 2 banks seperate). The second bank was beeing charged not by the charger directly, but inderectly via the battery selector switch in the cabin when placed in the "both" position. That explained why one set of batteries was always warmer and needed more water than the other. Live and learn.abe