Two batteries not close to each other

I am looking at adding a second deep cycle trolling battery so I can run 12V in parallel (I think thats the right term). The boat is a 2008 Triton TS18. There is not enough room to fit two large deep cycles in the rear hatch because the on-board charger is where the third battery would be mounted. No other suitable place to mount the on board charger. There isn't enough room next to the other deep cycle to fit two side by side. The trolling motor is a 12V M/K PwrDrv 55lbs 48" US2/AP.

Question 1: Are there any draw backs or don't do's to installing the 2nd deep cycle up front in a rod locker that I don't use for anything else. I could run wires from it back to the other deep cycle to get the parallel connection. The distance from one to the other would be +/- 7 feet. The back battery already has the connections w/fuses that go back up front to the trolling motor. It is all in the factory harness that I would rather not try to untangle.

Question 2: 6 or 8 gauge wire for the parallel connection?

Question 3: Will the on-board 2 bank charger that is already connected to the back deep cycle be ok for charging both deep cycles while in parallel? I think it is a 5 amp two bank.

Any other tips, ideas, or warnings I may need to know?

I would run either 6 or 8 gauge wires, red to red ,black to black and yes it will charge both batteries. I have mine wired this way.

Have you looked at putting the charger on the underneath side of the hatch lid?? That would give you room for the 3rd battery in the back and cut down on the amount of extra wiring you'll have to do.

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Originally Posted by wannabe fisherman

Have you looked at putting the charger on the underneath side of the hatch lid?? That would give you room for the 3rd battery in the back and cut down on the amount of extra wiring you'll have to do.

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That's what I would do too. I would keep the two batteries close together with short jumpers. You should be able to find another spot for your charger like under the lid of your deck, under the console, under your throttle controls, front side of the back deck(if you generally shed your sled, or build a rainshield for it if you don't). Somewhere, anywhere...imo.

I looked at the hatch lid. The on-board charger is not a long slim design. It is deep and more square shaped. The depth from the hatch lid to the top of the battery below the hatch doesn't leave enough room. Also, the hatch lid is only thin metal w/carpet on top and is part of rear deck that gets walked on ALOT. How would you mount the charger there without screws sticking up into your feet?

If I were to move the charger, how can I extend the leads? Just cut and splice close to the charger? The lead ends that attach to the batteries have inline fuses and connections that I don't want to try and duplicate. What gauge wire for those connections? Thanks for all the input.

I have the same problem,I have a sticksteer and there is no room to put another battery in the back,I can put one under the front seat but would have to run a 10FT jumper,is that a problem.

the biggest problem with parallel batteries is that they will tend to charge/discharge unevenly, which can lead to sulphation and stratification of the electrolyte. The extra length of the parallel wiring would only worsen this fact, technically speaking.

The batteries wouldn't last as long.

Catfan is the battery expert. I could be wrong.

I would not cut the charger wires if the unit is still under warranty.

If you do seperate them be sure to put another fuse or circuit breaker between them.

ok. instead of cutting and splicing closer to the charger, what if cut at the terminal ends and extend that part to reach. still add another fuse/cb? I have spent most of this morning looking for a suitable place to mount the charger. with the way the rear hatch area is configured there isn't another flat area to mount it. the last option I guess is to just remove the charger and install the 2nd deep cycle and then use a standard charger. was really liking the on-board convenience though. thanks again for any input

Have you considered putting your second trolling battery where your starting battery is? Then both trolling batteries would be together, your charger would stay in place, and your trolling motor battery harness would stay the same. Then you could mount your starting battery up front. Go to NAPA or a welding supply and buy good heavy copper welding leads to run your starting battery current back to a junction block. At the junction block, tie the starting battery leads, engine leads, and the other circuits which were on the starting battery all together. If your charger does 3 batteries, hook that in to. When you buy the welding lead wire, pick up the lugs for the connections. I like to solder mine, rather than crimp them. If you can't find a suitable junction block, you can easily make one with some brass bolts and heavy plastic for insulating. PS Make sure you buy some red electrical tape so you can identify positive from negative when installing the new starting battery leads.