On Guenevere, when we were prepping to go cruising I did NOT use an A/B switch.

I felt it was better to use 3 separate single throw, switches.
One is for my house bank.
One is for my start battery to engine.
And one is a combiner, if needed.

I have the house bank switch in the main cabin, and the engine and combiner switch in the aft cabin. I can cut energy for each system as needed, or use full power for each.

I also have an automatic combiner for charging ALL batteries from any source, alternator/shore/solar. AND, a Link-10 so I know how it's all working.

It's worked VERY good for us for quite some time.

Greg