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  • Charging two 12v batteries

    I’m being led to believe that when charging two 12v RV batteries that it’s more efficient to (see diagram) run a jumper from batt A Pos to batt B Neg and a jumper from batt A neg to batt B Pos. In many cases I trust the information I get here more than I get from YouTube videos. I’m thinking that if this were true then everyone would be doing it, so that’s why I’m asking.
    My current batteries are Duracell Ultra BCI 24M AGM 78Ah model SLI24MAGMDC. Please advise. TY.
    Dave and Sue
    2020 GD 2250RK
    2019 F-150 XLT, 5.0, 4WD, SB
    Curt 17500 WDH, 3.55
    GY Endurance, Dexter EZ Flex
    SCPO(SW) USN, (Ret), HP: Tampa Bay ⚓️🇺🇸

  • #2
    Connecting on battery positive to the negative of another battery will produce 24 volts from 2 batteries. You should have your batteries wired positive to positive and negative to negative. When attaching the charger you could attach the positive from the charger to one battery and the negative from the charger to the other battery, I think this is ok for led acid batteries but not sure though.

    Brian
    Brian & Michelle
    2018 Reflection 29RS
    2022 Chevy 3500HD

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    • #3
      The jumpers in your drawing place a dead short across the batteries and will result in smoke and glowing wire for a short while, then balls of molten copper flying around.

      Some folks suggest when the batteries are already in parallel to connect the charger leads to the positive of one battery and the negative of the other, but I’m not sure it makes a difference.

      John & Kathy
      2014 Reflection 303RLS
      2014 F250 SC SB 6.2

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      • #4
        Originally posted by Jkwilson View Post
        The jumpers in your drawing place a dead short across the batteries and will result in smoke and glowing wire for a short while, then balls of molten copper flying around.

        Some folks suggest when the batteries are already in parallel to connect the charger leads to the positive of one battery and the negative of the other, but I’m not sure it makes a difference.
        John, I think after reading your response that I’ve got the drawing wrong. We will see if anyone else chimes in. I suspect the ‘charger’ in our discussion would actually be the RV charging capabilities not a traditional independent AC charger. Pls see the attached.
        Dave and Sue
        2020 GD 2250RK
        2019 F-150 XLT, 5.0, 4WD, SB
        Curt 17500 WDH, 3.55
        GY Endurance, Dexter EZ Flex
        SCPO(SW) USN, (Ret), HP: Tampa Bay ⚓️🇺🇸

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        • #5
          Originally posted by Country Campers View Post
          Connecting on battery positive to the negative of another battery will produce 24 volts from 2 batteries. You should have your batteries wired positive to positive and negative to negative. When attaching the charger you could attach the positive from the charger to one battery and the negative from the charger to the other battery, I think this is ok for led acid batteries but not sure though.

          Brian
          Gotcha, thanks Brian.
          Dave and Sue
          2020 GD 2250RK
          2019 F-150 XLT, 5.0, 4WD, SB
          Curt 17500 WDH, 3.55
          GY Endurance, Dexter EZ Flex
          SCPO(SW) USN, (Ret), HP: Tampa Bay ⚓️🇺🇸

          Comment


          • #6
            Originally posted by Jkwilson View Post
            The jumpers in your drawing place a dead short across the batteries and will result in smoke and glowing wire for a short while, then balls of molten copper flying around.
            If we had a "Response of the Year" award, this would be near the top of my list!

            Forum moderators are not GD employees--we are volunteers and owners presumably just like yourself. Unless specifically mentioned otherwise, we have nothing to gain should you choose to purchase a product or engage a service we discuss on this forum.

            2017 Ford F-350 DRW, '19 315RLTSPlus

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            • #7
              Schiefswret The concept of hooking the charging leads to the positive on one battery and the negative on the other battery is in an effort to induce balance charging. This essentially forces the charger to output enough to charge both batteries as only hooking to one battery will result in the connection leads between the batteries doing the charging.

              Not really a fan of 24 V charging on 12 V batteries connected in series either. It's possible if you are running 12V components off one battery that the charging will only enter one of the batteries thus causing the cells to "boil" which can lead to an explosion. This happened at work with a 48V system running on 4 batteries. They were drawing 24V off of 2 batteries to run the control circuit and the charger was over charing the non used batteries resulting in overcharging and hydrogen gas production.
              Joseph
              Tow
              Vehicle: 2024 GMC K3500 Denali Ultimate Diesel
              Coach: 303RLS Delivered March 5, 2021
              South of Houston Texas

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              • #8
                Gotcha, thanks Joseph.
                Dave and Sue
                2020 GD 2250RK
                2019 F-150 XLT, 5.0, 4WD, SB
                Curt 17500 WDH, 3.55
                GY Endurance, Dexter EZ Flex
                SCPO(SW) USN, (Ret), HP: Tampa Bay ⚓️🇺🇸

                Comment


                • #9
                  Originally posted by howson View Post

                  If we had a "Response of the Year" award, this would be near the top of my list!
                  YUUUUUP 😀 agreed. Thanks Howard
                  Dave and Sue
                  2020 GD 2250RK
                  2019 F-150 XLT, 5.0, 4WD, SB
                  Curt 17500 WDH, 3.55
                  GY Endurance, Dexter EZ Flex
                  SCPO(SW) USN, (Ret), HP: Tampa Bay ⚓️🇺🇸

                  Comment

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