If he is trolling for crappie. I have a tracker v18 all fish started out with a 24 volt terrova and 2 31 series Walmart batteries and could only last 4 hours at 1.7 mph. I went to a 36 volt terrova and was good for about 6 or 7 hours but batteries were really drained didn't last long before I would have to replace them under warrenty. I now have a 36 volt ulterra with 3 golf cart batteries I can run at least 8 hours and still have over half my charge left. I did all of my fishing on Kentucky lake until just lately and have moved to JPP. If you can get 2 golf cart batteries it will last a lot longer. Just remember they weigh 85 lbs each and are just a little taller than a 31 series battery.
Don