I recently bought a 14' jon boat and a motorguide 54lb trolling motor (I can only run electric motor in the reservoir I wish to fish) I have 2 deep cycle batteries both are rated 120 reserve minutes at 70 amp hour draw, from the information I've found on the internet my motor is drawing at 38 amp hour max, I have 2 questions: 1) Should I run my batteries in parallel or single (which setup will last longer)? 2) How much run time will I have with the information I've provided if I run full throttle?

Thanks for your knowledge

1)  The more you cycle a battery between fully charged and discharged, the less it will last.  By wiring your batteries in parallel, you will be saving them from such a severe discharge every time you use the motor.  I would think that would make them last longer.  I have no actual experience with this, I am just using what I consider to be "common sense".

2)  Maybe when I have time to do the math

At a 38 amp draw one of your batteries will run your motor for 1.8 hours at full throttle. If you wire them in parallel they will last 3.6 hours. At the average trolling motor speed of 5~6 MPH this gives you a range of 15~20 miles. If these batteries are new, I would wire them in parallel and treat them as one battery for use and charging. Just make sure you get heavy enough wire to connect them together. I would think 4 gauge should to it. Any auto parts store will have that needed cables.  A 10 amp charger will take 14 hours to charge these batteries, wired in parallel, to full charge from dead. Make sure you keep the batteries full of distilled water before you charge them.

Oh!, Make sure you keep oars handy.

Here is a good read for everyone about boat batteries.

http://www.uuhome.de/william.darden/