Lu Powell wrote:
I recently bought a used Champion brand bass boat. It has a battery
dedicated to the trolling motor that is not wired in to the charging
circuit for the cranking battery. The trolling motor battery gets
charged at home prior to a fishing trip.

Is there a simple fix that would let me charge both batteries at the
same time while on the water, and use the trolling motor battery
without draining the cranking battery?

It's not likely that you would run your engine long enough to
significantly charge the deep cycle trolling battery. Small outboards
often don't have the charge capacity to charge two batteries. You can
test the capabilities by temporarily paralleling the batteries with
jumpers. I don't need to remind you that you need to be careful about
shorting things out and creating sparks.