# Batteries in parallel? with switch? on board charger?



## RivRunR (Mar 10, 2010)

I've searched the forum, but haven't quite found the answer to my questions, or if I did I didn't know it...I'm not great at the electrical stuff...

I currently run 2 separate, identical Interstate series 29 marine deep-cycle batteries:
1 for a 12V MK Edge 40 bow-mounted TM
1 for the cranking battery on a 1980 Johnson 70 (has "alternator"), plus lights, bilge, livewell, and depth finder.

Typically I run the OB very little, usually no more than 10 minutes just to get to the spots I fish, then it's several hours on just the trolling motor, then another 10-15 minutes back to the ramp. So, the trolling motor battery gets a lot more use, sometimes to the point that it dies, and it has to be charged after every trip, but the cranking battery rarely needs charging. I have a good battery charger (but with no "deep-cycle" setting), problem is I have to park the boat outside, and can't always charge the batteries after every trip because I don't want to leave the charger out in bad weather.

So, what would be the best way to set up my batteries? What I'd like is a set up where I can maintain the most charge on the TM battery, but never lose the ability to crank the OB...pull start isn't really an option...I've tried it. If I run the 2 batteries in parallel I would lower the draw on the TM battery, but couldn't I also draw down the OB battery to the point where it won't crank? From what I've read here I think that I could cure that problem with a switch, and point it to "both" when the OB is running (and when it's on the charger), but again, I run the OB so little that I don't know if I would get much out of that set up, plus I'd probably forget to flip the switch every time I crank the OB anyway.  And would there be a problem when charging them rigged in parallel if the OB battery has so much more charge than the TM battery?

I guess another option would be an on-board charger, but I'm completely ignorant about how those work, so I have to rely on you guys whether it would help in my situation. I also run another depth finder on the bow from a small, mower-sized battery, but I expect that with the size difference that it is kind of out of the on-board charger equation?

Anyway, sorry to be so wordy, but I wanted to give the full picture, and I would *really* appreciate your suggestions on the best set up.

Thanks!


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## redbug (Mar 10, 2010)

On board chargers are built to be out in the elements. most can be submerged without any harm. 
That is what I would do I would look at a dual bank charger that has 5 to 10 amps per bank.
Running the batteries in parallel won't drop the draw your trolling motor puts on the batteries but will add to the amount of time you spend on the water.


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## russ010 (Mar 10, 2010)

Definitely go with the on-board charger... that will save you $$$ in the long run. Just ran an extension cord out to your boat - plug it in and forget it. The on-board that I have is a Guest 2611 model. 2 banks (meaning hook ups for 2 batteries) and they each deliver 5 amps to each battery. It takes my batteries about 4-6 hours to fully charge after a hard day on the water. Each cord from the bank has 2 wires - a positive and a negative - you hook up each one to it's post on the battery. That's really all there is to it. I've actually got 3 of those chargers on my boat - and 5 batteries. One of the batteries has both banks feeding it, until I get another battery.

Cabela's usually runs a good sale on them. They are regularly priced at $119. But the first 2 I bought at once for $90. The last I bought just a few weeks ago for $60. They had a really good special running on them at that time. Here's the link to them - https://www.cabelas.com/cabelas/en/...en/common/search/search-box.jsp.form23&Go.x=0. 

You can put them in parallel... I did that on my other boat and the run time was a bit longer. You just want to make sure you leave enough juice for your big motor to start up.

Have you thought about maybe adding a 3rd smaller starting battery for your motor? You don't need a deep cycle for that. Just a regular ol' car battery will do the trick.


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## cavman138 (Mar 10, 2010)

so if your batteries are both hooked to the on board charger then power will be pulled from both batteries equally?


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## fishbone (Mar 10, 2010)

First of all, you don't want a deep cycle battery on the outboard. You want a high output cranker. The on board charger is the way to go. Each battery will draw, or be provided, the voltage/current needed (separately) from a 2 bank charger.
I just finished installing a 3 bank charger today. Battery 1 = engine, bow fish finder and accessories, battery 2 = trolling motor, and battery 3 = main cockpit Humminbird unit (and as a back-up to battery 2 trolling). Each battery is charged separately from the charger.
If you buy a new battery for the engine, then a 3 bank charger, you would have a trolling motor back up.


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## redbug (Mar 10, 2010)

cavman138 said:


> so if your batteries are both hooked to the on board charger then power will be pulled from both batteries equally?


No... A two bank charger is like having 2 separate chargers in one package. if you hook the batteries in parallel they will draw equally.


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## robr3004 (Apr 1, 2010)

Hey guys, I'm new to the forum and it's a great wealth of info. I'm picking up a Tracker 1436 on Saturday and I am in the market for an on-board charger to charge 2 12 volt batteries connected in parallel. My question is if I get the Guest 2 bank 5/5, can I connect both banks to the batteries while they are still connected in parallel or do I need to disconnect the parallel and charge them separately?


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## russ010 (Apr 1, 2010)

robr3004 said:


> Hey guys, I'm new to the forum and it's a great wealth of info. I'm picking up a Tracker 1436 on Saturday and I am in the market for an on-board charger to charge 2 12 volt batteries connected in parallel. My question is if I get the Guest 2 bank 5/5, can I connect both banks to the batteries while they are still connected in parallel or do I need to disconnect the parallel and charge them separately?



you can leave them hooked up like they are


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## robr3004 (Apr 1, 2010)

russ010 said:


> robr3004 said:
> 
> 
> > Hey guys, I'm new to the forum and it's a great wealth of info. I'm picking up a Tracker 1436 on Saturday and I am in the market for an on-board charger to charge 2 12 volt batteries connected in parallel. My question is if I get the Guest 2 bank 5/5, can I connect both banks to the batteries while they are still connected in parallel or do I need to disconnect the parallel and charge them separately?
> ...




Thanks russ010, just ordered the Guest 2611 from amazon for $96.


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## russ010 (Apr 1, 2010)

robr3004 said:


> Thanks russ010, just ordered the Guest 2611 from amazon for $96.



no problem man - and that's a good charger too... I've got 3 of them on my boat :lol: 

I paid $60 each for mine... cabelas will run a sell every so often where they have them for $90, but if you look around the page there will be an additional $30 off coupon code


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## Bugpac (Apr 1, 2010)

If you parallel battery's they will not draw equally unless your load is out to both of them, be sure to ground to one battery, and take positive from the other.. if you take both from one battery it will pull the load from that battery faster, as there is the least resistance..


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## robr3004 (Apr 1, 2010)

$60 Bucks....nice. Wish I could wait around for that sale. Luckily I have an amazon account so I get free 2-day shipping. Now off to plan how I will wire the boat. Shouldn't be too hard, just 2 trolling motors and a fish finder.......for now.


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