He's not talking about a battery switch, he's talking about a diode isolator that splits the alternator charge to go to two different battery banks. I doubt it is the alternator, unless it is putting out excessive voltage or it is puts out more amps than the isolator is designed to handle, which would be easy to spot on your voltmeter or amp meter. Most likely it is just a bad isolator problem. The diodes in them are prone to overheating
, hence the huge heat sink they are mounted to. However, I've seen some boats with the isolator mounted in a very hot spot, like in the engine
room, which is guaranteed to not be good for the isolator.
Besides, isolators are not the best way to charge two battery banks due to loss from heat and problems with getting the right amount of charge current
. Better to use something like a battery combiner (Yandina), or a trickle charger
like the Echo Charge or the Trik-L-Start.