One battery will be more than enough for either trolling motor. Bigger is better unless you are trying to keep the weight down. I say this from experience, you will be just fine on the lower settings and it will run all day like that. When there is a little wind, it's great to be able to hold that little boat where you want it with that trolling motor. It's also fun to throw a wake with it while chasing schooling sand bass.
@Msharktwit if you are on the Twitter