OK, so I have a trolling motor like you describe. I bought it for effortless Canadian canoeing in the sea because a petrol OBM was a bit too heavy to hang off the side of the canoe and also the trolling motor is beautifully quiet on the river.
I guess there are any number of questions, firstly, why?
Where do you wish to use it, and for what?
I'd not use it on a SIB in the sea, it simply doesn't have enough grunt.
I have a 55lb Minn Kota Riptide. Perfect for what I wanted. And used as a backup in the SIB if I can be bothered to take it.
I went 55lb as that's the highest you can go at 12v. Higher and you need a 24v system.
I'd get 3ish hours out of a 110ah deep cycle battery (about 25kgs).
It would push the canoe along at about 6kts with 2 adults and 2 kids on board in favourable conditions.
Once used it to push a 14ft speed boat back to harbour against wind and tide, was going about 1kt and at times I wondered if we would make it back!
If you intend to use in the sea (I'd not recommend it), make sure you get one designed for the sea.
For the price of a good trolling motor and battery you could have a much more powerful 2 or 3hp OBM, and that's new!