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Two 6v batteries better than two 12v?

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  • Two 6v batteries better than two 12v?

    I was talk to a guy at the docks and he said that he replaced his three house batteries with two 6 volts batteries in series. He said that they will last as long at four 12v in parallel for house batteries. He did say to keep one 12v for the engine battery. Has anyone heard of this?


  • #2
    Re: Two 6v batteries better than two 12v?

    It comes down to simple arithmetic. Two 6v 400cca batt's in series will last the same time as one 12v 800cca. If the amps are not equal, the higher number wins. A 6v batt is usually much bigger than half of a 12v one.

    A lead-acid cell is good for a nominal 2.0 volts. 3 of them makes a 6v batt, 6 will make a 12 v batt. The actual power is up to the number of, and the size of the plates.

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    • #3
      Re: Two 6v batteries better than two 12v?

      I haven't heard of them being used as cranking batteries, just for deep cycle purposes. Specificly, using large golf cart 6V batteries in series to get more reserve than typical 12v DC.

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      • #4
        Re: Two 6v batteries better than two 12v?

        Cost per reserve minute may surprise you. In other words one big deep cycle may be much cheaper than two golf car batteries for the same theoretical run time.

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        • #5
          Re: Two 6v batteries better than two 12v?

          Well, it is certainly too expensive for my needs.

          I just looked at a Trojan T-145 6V and its rated at 530 minutes @ 25amp. Two in series would be the same rating? A group 31 DC would typically be around half that.

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          • #6
            Re: Two 6v batteries better than two 12v?

            They would be used as house batteries not for starting or running the engine. So what everyone is saying is stick with two 12v deep cycle batteries?

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            • #7
              Re: Two 6v batteries better than two 12v?

              Originally posted by themaniam1 View Post
              They would be used as house batteries not for starting or running the engine. So what everyone is saying is stick with two 12v deep cycle batteries?
              Generally two 6v in series will be a better setup than 2 12v in parallel. As mentioned, two 12v will probably be cheaper but good quality 6v batteries can last for years.

              I know more than a few cabin cruiser owners that have switched to a 2x 6v golf cart batter setup as their house power and have been very satisfied.

              It's all about price per amp/hour really. If you can find a good 12v 8D battery with the same amp hours as the two 6v you're looking at then go for that.
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              • #8
                Re: Two 6v batteries better than two 12v?

                Originally posted by Silvertip View Post
                Cost per reserve minute may surprise you. In other words one big deep cycle may be much cheaper than two golf car batteries for the same theoretical run time.
                That would be pretty tough to occur unless the 6V batteries were really small. Basically, every motor home and most large boats use 6V batteries for house batteries. It is the best way to go for truly deep cycle.

                Also 2 12V in parallel are not nearly as good as having 2 6V in series. One bad cell will pull both batteries down when they are in parallel. This will have a detrimental effect on the good battery keeping it from getting fully charged.
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                • #9
                  Re: Two 6v batteries better than two 12v?

                  Originally posted by wire2 View Post
                  Two 6v 400cca batt's in series will last the same time as one 12v 800cca.
                  Please check that.

                  Two 6v 400cca in series will deliver 400cca at 12 volts. Two in parallel will deliver 800 at 6 volts.
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                  • #10
                    Re: Two 6v batteries better than two 12v?

                    Originally posted by RickJ6956 View Post
                    Please check that.

                    Two 6v 400cca in series will deliver 400cca at 12 volts. Two in parallel will deliver 800 at 6 volts.
                    Dang! You're right, Rick. It comes down to the product of the numbers being equal.

                    My post *should* have read "2 6v 800cca's in series are the same power as 1 12v 800cca". Thanks for bringing it to my attention.

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                    • #11
                      Re: Two 6v batteries better than two 12v?

                      And for what we are talking about here is for a house battery we don't even care about CCA. We care about the capacity in Amp Hours. CCA is the ability to deliver a lot of current. You can have low CCA compared to another battery yet have WAY more capcity.
                      1998 Wellcraft Eclipse 24 Cuddy
                      Volvo Penta Duo-Prop 7.4L "LK"

                      2006 Sun Tracker Party Barge 21
                      Mercury 90 4-Stroke FI
                      "Common sense is not very common"
                      "Failing to prepare is preparing to fail." -- John Wooden

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                      • #12
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                        Re: Two 6v batteries better than two 12v?

                        One of the biggest reason out here that the houseboaters switch to the 6v batteries is that they cycle better and longer than a 12v battery does.

                        Meaning if the battery is "deep cycled" discharged down to 10.7v or so, the 6v batteries will withstand this for a longer period of time loosing less of their fully charged capacity.

                        Not sure if this is totally correct, but practical application has shown to be true.
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