Thanks for all the feedback so far. Boat is single engine with a single alternator. One bank (2 batteries) leads into a distribution block with a positive wire. Out of the distribution block comes 2 positive wires, each going to one amplifier.

On the other side of the boat are two batteries that I assume are used to start the engine and run all of the lights, gauges and other accessories.

To complicate things further, the boat has a three bank on board battery charger/converter, although I don’t really understand how it is hooked up. But it does seem to work fine:)