I have a 16 ft aluminum v hull and I have a 40Lb thrust Minnkota trolling motor.  How many batteries should I have for my trolling motor?  I usually fish lakes but I want to start fishing on the Mississippi River and on an electric motor only lake this year.  I have heard that the current effects the battery.  

I am sure your trolling motor is only on a 12V system. But, if you

have the room, I would put an extra battery in the boat just in case.

JT Bagwell

 I have a 50 lb. on my boat and normally carry a spare battery.  I haven't run it on a river or anywhere with heavy currents yet, just on area lakes.  From what I have seen crossing the Mississippi there are times the current looked mighty strong.  

 In heavy winds with rough water I have seen one of mine and others get pretty weak when running mostly on the higher settings.  I know I have had to swap out a time or two, but some of those times might have been do to an older battery or not being fully charged to begin with on some trips.  I believe the operating time chart gives about 1.5 hrs. for mine on high.  I don't think I would want to risk running that river with only one battery and no other motor for back up on an all day trip.

River current doesn't affect battery life but pushing your boat agaist river current draws more power. You can wire two batteries in parrallel (+ to +)and increase the length of time you have suitable power. If you have a 12 volt system do not wire the batteries in series (+ to -) because that doubles the voltage and will fry your TM.

Adding batteries adds a lot of weight so be sure you stay under your boats total weight limits for safety.