the OP made a -good question. I am curious about it too
I've had the red wire coming out of my alternator disconnected once, with the engine runing, for over 1 hour, when I realized the batteries were not charging.
I looked around and found the wire disconnected at the alternator.
Nothing was damaged..the bateries, or alternator.
I have on other occasions, maybe once or twice, switched from Bat 1 to Bat 2 with the engine runing and nothing happened..
was I lucky? or is my engine good?
So one should not have any thing that charges the bateries when selectin 1, 2 or both??
I never did that in my whole life an nothing ever hapened.