JohnSv:
You did not say what HP your motor is which can make a difference in amps needed to start.
Ya, one good battery would do the job but you "should not" use your starting battery for the trolling motor unless you have a manual start option on your motor, Shit happens, as they say, and you do not want to end up in a position where you can not start the motor because you used up the battery with the trolling motor in some unforeseen circumstance.