OP here, thanks everyone for your help. I have the bracket made for the kayak and I am going to try this battery. My thinking is this, I don't mind paddleing, the rivers we fish are what I would call pool and drop. There are class 1 and a few class 2 rapids with pools of water in between. Most of the pools are short with a little current flowing so we just drift along and fish (we use spinning rods, we do not troll). Some of the pools are longer and the current will not pull you along so paddleing is required, this is where I would be using the trolling motor, so 10 minutes at a time tops. If the battery goes dead, I would just have to finish up the trip with the paddle.
As far as turning over, I have done that one time in the last five years and it was my fault. I tried to paddle around a downed tree in a rapid and went into the tree and flipped (I now portage around those).
Another thought about the life of the battery. If I pull the battery down below 50% and shorten the life of the battery, that is no big deal to me. 8 trips on a $50 battery is $6.25 per trip. My fishing lures are $5 yo $8 each and I normally lose 2 or 3 on each trip so a new battery every 8 trips would not be an issue.
Thanks again everyone for your help.