I agree with Mike because in this day and age you have many choices for REGULATED chargers/ maintainers which will properly charge and regulate batteries. All isolators have some voltage drop and will not charge the batteries equally, and can not "sense" which or if either battery is low.
Isolators were always a problem for me, as "up here" there were two boat explosions with isolator equipped systems, here is the problem:
In an alternator/ engine situation, the regulator only senses the main battery. The second battery also gets charged, but the regulator "reads" off the main
What can happen is that one of the two diodes in the isolator can open, and now the regulator says "hey, the main batt is going dead, let's charge to beat hell." And so the voltage regulator ramps up, and is charging the pee waddin' out of the SECONDARY battery.
I'm not sure one charger would do any different.
