How to hook up 2 batteries together?

[charliegiggles]

Hi,

I originally purchased 2 seperate batteries so that my 1979 70HP Mercury outboard would be isolated on one with my trolling motor / trim and all accessories hooked up to the second battery.

I've run into a problem where I'm wearing down my deep cycle battery pretty quickly running pretty much everything off of it and would like to combine both batteries together so that the outboard motor charges not only the first battery it's connected to but also the second.

I was told to hook a proper battery guage wire from pos to pos and neg to neg. Is this the best way to do it?

I wouldn't want to burn any of the charging components on my outboard "rectifier/stator" by making it work too hard charging both batteries however would really appreciate the batteries being charged simultaneously when I am using the outboard motor?

Thx as always....

 

[jtexas]

Re: How to hook up 2 batteries together?

Not sure about those mercs, but a 3-cyl OMC alternator is only 6 amps - it won't replace the juice used by the trolling motor without running hi-speed for a loooong time.

What I do, and pretty much all the fishermen I know, is run lights, livewell, bilge, fishfinder(s), off the cranking battery, which is able to keep up with that demand, and the t/m on its own. I added a second trolling motor battery, connected as you described ("parallel connection"), to get 2x the run time on my 12V trolling motor. When I use the bait tank I usually hook it up to the T/M batteries cause I don't use the T/M as much when bait fishing I'm usually anchored or drifting. Also carry jumper cables, just in case I need to jump myself.

Having said all that, parallel as you described (+ to + and - to - ) is how you would do it if you were going to do it. Not sure if you would get the best result, as the batteries aren't matched as to capacity and state of charge. Also, the accessories including the T/M would drain both batteries simultaneously, just not as fast as they would drain one.

 

[Chris1956]

Re: How to hook up 2 batteries together?

Charlie, The output of your alternator is only about six amps. It will therefore not charge up your deep cycle battery quickly. I think the best you do with that setup would be smart to reserve one battery for starting and accessories (they shouldn't take much current), and use the other for the trolling motor. You can install a battery combiner between the two batteries, such that when the starting battery is fully charged, the motor will start charging the trolling battery.

 

[burroak]

Re: How to hook up 2 batteries together?

There is a lot of good info on www.cmsquick.com. Just click on "technical" in the port menu.

 

[charliegiggles]

Re: How to hook up 2 batteries together?

Thanks for the responses!