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Wiring question for new charger and AGM batteries-gctid807247

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  • Wiring question for new charger and AGM batteries-gctid807247

    So I bought the boat 5 years ago, and still have the batteries that came with it. I'm replacing the 3 group 24 flooded cell batteries (1 starting and 2 in parallel for house) with marine AGM Duracells (group 34 for starting and group 31s for house). I am also replacing the non functional 2 bank charger with a NOCO Gen 3 triple bank charger. I did the triple bank since there are 3 batteries. After doing a bit of research, I believe that it all should be wired up as shown in the diagram.

    Note - All 3 batteries are 12V, which is why house bank is in parallel. Charger has 3 banks at 12V each with 4 amps each bank (12 amps total).

  • #2
    Not quite.

    The charger likely has one common ground so you would run that to a good common ground. Check with the instruction manual for that.

    Your house batteries are connected correctly but you should run the positive to one battery and the negative to the other so the power runs through both batteries 'as one'.

    Again check with the charger manual, but you probably will use two of the three banks, one to the starter battery and the other to the house set.
    1989 Avanti 2955
    460 Cobra


    • #3
      This is straight off of NOCO's website showing how to wire 2 batteries with a dual bank charger. It shows 2 batteries separate banks, 2 batteries in parallel, and 2 batteries in series. The charger has a positive and negative lead for each bank.


      • #4
        I don't think you should use two different charging circuits on a parallel battery bank, I would treat your house bank as one battery and as car2n suggested wire up the positive to one battery and the negative to the other. You could research the charger and see if it will work but my thoughts are that it has three separate charge circuits that should not be combined. It would be nice if you could though, and get double the charge current. I bet it will take a week to charge your house bank with 4 amps.
        1990 3888 Bayliner, Twin 351's


        • #5
          One combined bank needs only one + lead from the charger. This is an image that Rick has posted many times, it's how I've wired mine, it keeps things nice and tidy.

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          • #6
            I just spoke with NOCO support and sent them the diagram I made. They concur that is the way I should wire up my 3 batteries with their charger I purchased. It might be different on other chargers, but they said that all 3 circuits are isolated from each other. I went with the 4 amp per bank instead of the 10 amp as I bring the boat home the night before we launch and plug it in just to top off the batteries. I've never had an issue with running out of power. When I pulled the batteries, all three were group 24 rather than 27. The 31's I'm putting in for the house bank are almost twice the size! The dead charger I'm pulling out was a dual bank 5 amp.


            • #7
              Your system will work as shown in your schematic, however, charger "charge" leads should make their connections to the rear MBSS terminals #1 and #2 in lieu of going directly to the batteries. This avoids the potential Rat's Nest that we often see, plus it also helps with battery R&R in that we remove/replace battery cables ONLY (no wires to become confused with)

              The charger's Negative should connect to the "system negative common"..... i.e., the engine block as shown in my schematic that Dave posted in post #5.

              The 3rd charge lead may be combined with one of the other charge leads. See your Charger Installation and/or Operation Instructions. As is now, even though each connects to a 12 v battery (that is in parallel with the other), the two charge leads have essentially been combined.

              I took the liberty to make a few changes to your image..... no offense.

              Rick E. (aka RicardoMarine) Gresham, Oregon
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