Since there has been so much talk about charging to banks from a single engine here was my solution years ago. BEP Marine, I think now owned by Blue Seas sells a cluster in many configurations for single, twin and triple engine installations with charge relays and isolators, that in most cases don't require rewiring to install them.

You end up with an on/off switch for each battery, a parallel switch to charge a weak battery in the event one gets run down and you can't start your engine and a charge relay that will give charge priority to your start bank and then charge your house bank when the start bank is fully charged. It will then isolate the banks when your engine or engines are shut down.