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Adding 3rd battery

broncomatt

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I currently have 2 batteries on my 496 HO with the standard 2 battery switch. I have my stereo and amps wired direct to the 2nd battery to protect myself from draining the 1st battery and getting stranded. The issue is the 2nd battery seems to drain pretty quickly when listening to the stereo so I want to add a 3rd battery to allow for more stereo run time. I searched all over for info but haven't found anything that is really clear, does anyone have a wiring diagram on how I should do this? Is it something that my alternator can even handle charging another battery?

Any input would be greatly appreciated.
 

STV_Keith

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If you want to continue to use it as is, just parallel the new battery with the old #2 battery. That is, put positive to positive and negative to negative. That said, it's generally said to only connect two batteries of equal age. In that case, you may want to move your old #1 battery over to the stereo/house bank and add the new battery as #1 to start the engine.

If you run with the battery switch on #1, then battery #2 (and #3) don't get charged at all, unless you have an ACR (automatic charging relay) or some other wiring in the system. If you run on all, then you are effectively connecting all the batteries together. Personally, I'm not a big fan of that. I'd rather have an ACR which will allow the engine to charge battery #1, then once it's full up, it will charge the other bank, all the while the battery switch is on #1 only.

Also, if your stereo is wired directly to battery #2/#3, then you might want a simple ON/OFF battery switch on that. That's what I do.
 

broncomatt

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Thanks for the input! That actually makes it really clear. I did have a few more questions...
1. what ACR are you using? I looked online and found these http://www.bluesea.com/products/category/Automatic_Charging_Relays - not sure which one is best?
2. I watched a video that says I should switch out my on/off battery switch to a 4 post switch, and then showed a black with yellow ACR, is this what you are using?
3. you mentioned installing a ON/Off battery switch to cut power to the battery my stereo is wired directly to? Where did you mount yours at and do you have a link to the one you are using?

Thanks again for the help!
 

STV_Keith

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Feelin Nauti

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I run 3 batteries myself and found the easiest way was to run a 3 bank battery isolator and 1 battery switch. The battery isolator makes sure all 3 batteries are getting charged when the engine is running regardless of the battery switch position and doesn't allow batteries to drain each other. I run the stereo off the 3rd battery only,batteries 1 & 2 are for starting and emergency back up start. simplest way to disconnect the stereo battery when in storage is to use a battery terminal cut off switch on the ground terminal. i also have a Promite 3 bank marine battery charger mounted in the back so all i have to do when i get home is plug it in and it maintains the batteries untill the next trip.
 

headshothills

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I run 5 batts... Actually 6 if I wanted, but dont have a 6th batt in the hold down... 1 perko switch.... 2 of the PC1500's for the motor and 3 of the 31 series... The 2 PC1500's are on 1 side, and the other 3 are on the other, but I always leave the perko on Both, can run the stereo all weekend and all day without issue.... 3500 watts old school RF amps....

I like the isolator deal, that is guaranteed no dead batts for start up and its hands off so no opening the hatch and flipping a switch either....
 

Flyinbowtie

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Check out these isolator/combiners...

www.hellroaring.com

I've had one of their units in our boat, (3 Optima deep-cycle/starting, two on the load for the engine and stereo, one in reserve) for several years and put 2 others in boats for other folks, these things are great for saving a battery in isolation for starting and controlling the charge output of the amp so that you don't wind up trying to charge 3 or more batteries at once, sucking the life (brushes, diodes, etc) out of your alternator.
None of my friends have complained, and have recommended them to a bunch of others. No complaints from anyone.
 
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