So I was given a Jon Boat for some work I did. Its a 12'. My hous backs up to the lake. Im looking 30-40# to put a trolling motor on it. Im having trouble figuring out batteries. I know I need a deep cycle. But I saw a small one at academy for $50. What I liked about it was the small sive and weight as I will be dragging down there. My question is what do I need to be looking at as far as what will run the trolling motor the longest.

Go with the largest Reserve Capacity deep cycle battery you can afford, fit in your boat and carry down to the water.

get a grp 27, not light but will run that size for hrs at high speed. if you are only using a trolling motor for power you need a big battery to guarantee you get back. I would get a 50# as well, if wind comes up a 30 may not have enough to hold you where you are and a 40 might be real slow going, a 50 on a 12' john should give you plenty to do what you want.