paulmar your right. i was worried about the diode connectiing across both banks but i can see now that the diode would block the discharge of the starter battery. the nicest system i've installed in the past is one that has a solenoid that only energizes when the main
batteries are showing charged. it then closes the solenoid and charges the other bank hooked up with the solenoid. when the main bank loses a certain set voltage,say 12.5v, it disconnects the solenoid. the nice thing about this is there is no voltage drop in the curcuit unlike a alternator splitter.