"To have the outboard engine a
"To have the outboard engine also charge the trolling motor battery, it is simply a matter of running cables from one battery to the other.
That is from one battery's positive terminal post to the other battery's terminal positive post, and also from the negative post to the other negative post HOWEVER.......
You do not want the trolling motor to be drawing voltage from the outboard engine battery when you're operating the trolling motor SO YOU WOULD WANT a disconnect switch between one battery and the other at some point in the positive cable circuit.
When running the outboard engine, have the switch engaged.
When NOT running the outboard engine and you're running the trolling motor, have the switch disengaged.
There may be an electronic relay setup that I'm not aware of which can be used in place of a switch. If so, hopefully someone with that knowledge will jump in here to explain."