I am installing a battery switch in my boat, if I want to use one of the
trolling motor batteries to start the engine.
It is a center console that is also used in the salt water besides bass
fishing.

The ground of the trolling battery has to be strapped with the starting
battery ground, which grounds on the engine.
Will this cause any ground loops or problems with corrosion etc.?

I did not think so but I would like advice.
Thanks in advance.
Joe