parallel batteries

[fowlmouth]

any reason not to run trolling motor batteries in parallel? boat has two tm batteries and the previous owner just switched the cables from one to the other. it is a 12v trolling motor but I think if you parallel the batteries they will run longer/stronger than if they were run separately, does this make sense?

[canvsbk]

yup, makes perfect sense.

[djkimmel]

I've never tried it, but that is the main deal with parallel - you get more time for the same voltage. Just make sure you aren't doing something else that would have a problem with this. The only thing that comes to mind is charging. I've seem some diagrams that show the positive charge on one battery and the negative on another, but don't take my memory for it...

[smbassman]

As long as both batteries are in roughly the same condition, it's no problem.  If one battery is older and possibly has a weak cell or two(or three, or four....etc.) then it could become a parasite to the good battery when hooked up in parallel.  If you get about the same performance out of each battery when using them seperately, then you will be fine in parallel.

[gnewski5]

This will be my 4th season since connecting both batteries togather. I am so glad I went to this system. The charge lasts much longer. I can fish 2 straight days (8 hour tournys) without recharging, and still have plenty of juice. Plus with them hooked togather when recharging they both charge at the same time. I've had some tournys that I only used 25% of the batteries in 8 hours. Thats relevent to the conditions though, wind, current and what your trying to fish.

I just ran up to the local battery dealer and they made me up some custome cables to fit my boat. As I recall, it didn't cost very much either. As smbassman said, the batteries have to be close to the same condition or the bad one will hinder the good one.

[fishon1219]

When I had a 12 volt system I ran my batteries in Parallel as well and never had a problem with rundown batteries at the end of the day. Also I just hooked up the charger to one battery and both would charge. The only way to go with a 12 volt system is parallel

[djkimmel]

Couldn't remember - seemed like someone once recommended to me to charge them together, but I would recheck with one of my battery sources before I told anyone to do it.

I forgot the part about the batteries needing to be about the same age, same size, to do the parallel - glad you all caught it.

[bshaner]

Let me get this parallel thing straight before I do it.  I know how to parallel the batteries, positive to positve, negative to negative.... what is the recommended way to hook the TM to them?  positive to one and negative to the other or both pos and neg to the same battery?

[fowlmouth]

I'm pretty sure it's to connect them to opposite batteries, + from one - from the other.

[smbassman]

Just use 8 (or larger) guage wire to make short jumpers and connect pos. to pos. and neg. to neg.? Then connect the TM wires to either of the batteries.  You can also connect TM to the pos. of one battery and the neg. of the other.  It really doesn't matter as long as the jumper wires are large enough to have negligable resistance.

[bshaner]

Thanks guys.

Brian

[Bender]

I plan on changing my boat over to a parallel circuit also soon, this is good information. One question I have is where is a good place to get a battery meter to mount in the console?
I would like to be able to keep an eye on things even though I never have time to stay on the water for more than a few hours and make sure I can always get the big (little in my case) motor to start. How far down do you let them get before the big motor won't turn over? I am a newer boat owner so any information is helpful, thanks!

[fowlmouth]

I think you can get a meter at BPS. I run three batteries, 2 for the trolling motor and 1 for the big motor/livewells,gps, etc. so i don't how far down they can go b4 you're looking for a tow. I like this setup because you can jump start off the trolling motor batteries if need be. I ran my boat 2 full days without having to recharge the parallel batteries and they still showed 700cca on my load tester when I got home. 
when I hooked up my batteries I went and bought a 30" battery cable and 3 replacement clamps at Advance, I just cut the cable in half put the new clamps on and was ready to go, coat me less than $10.

[djkimmel]

I only know in approximate volts - 12.6 and above is a full charge I believe.

12.4 and above is at least 75% charged and should start most smaller motors fine. Larger, more modern motors, especially DFI's, have a large CCA requirement to safely start them without potential damage.

This is with a healthy battery. An older battery or one going bad can show a full charge right after it is charged, but fail a load test, and therefore not start or struggle to start larger motors or run items for very long.

Recommendations are to recharge a battery after it goes below 75% recharge (assuming healthy again), but you may be able to start a moderately sized outboard okay down to a 50% charge or so - 12.2 V.

Truly, I have been told by several companies' outboard techs that repeated starting of the new high-tech larger outboards with a battery very far below approximately 1,000 CCA can damage the outboard. I don't understand it well, but it is something to be aware of and consider.