That's a sizeable boat to be pulling with just one 12 volt battery, is the TM a 55# thrust? You can run two 12 volts batteries in parallel to give you more trolling time, best to be the same group size battery, brand and age. Also, the larger the group size the better, I would probably go with at least group 29's or better yet 31's if you got room for them. Or if your serious about pulling cranks may even look to going up to a 24 volt TM in the future, I had a 24volt Ultrex on a 16' G3 40HP running on two Exide 31's and could troll for up to 10 hours straight and your boat is bigger than that.