I have my batteries set up with the 7600 between a house bank and a starter battery. There are different ways to do it but the way I have it wired, the house bank is charged by shore power, the starter battery is charged by the alternator. When either battery is above 13.5V for at least 30 seconds, the house bank and the starter battery will combine, when the voltage of both batteries falls below 12.7 for 60 seconds they will be isolated. Those are the factory settings, they are adjustable on the 7600. There is also an undervoltage lockout feature (4V) to prevent putting current into dead / damaged batteries or a short.
So, if I'm motoring, the alternator will charge the starter batter until it's above 13.5V, then the ACR will combine the banks to charge the house batteries as well. When I shut off the motor to sail, using power for instruments, nav
lights, etc, the ACR circuit will open to isolate the batteries as soon as the house bank drops below 12.7V, so the starter battery is kept in reserve. When I get back to the dock and plug in, the charger will charge the house batteries until they are above 13.5V, then the ACR circuit will close and allow the starter battery to be charged as well.
You can check the
installation instructions for the product (see the section on sensing both batteries) or contact Blue Sea for advice. They were great for helping me set my system up.