I'm not very electrical savvy but I was told that two 6 volt batteries in series offers more storage power for my Vision 32. Has anyone gone this route?
Two 6 volt batteries instead of one 12 volt
- Thread starter LeeJune
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Two 6v batteries in parallel will increase capacity but will still be 6v. Two in series will allow the batteries to put out 12v but the same capacity.
Some ballpark numbers:
6V golf cart batts have typically about 225 amp hours .. so two in series give ya 12 V and 225 amp hours.. A size 31 deep cycle 12V has typically 110 amp hours .. two of those in parallel give ya 12V and 220 amp hours..
6V golf cart batts have typically about 225 amp hours .. so two in series give ya 12 V and 225 amp hours.. A size 31 deep cycle 12V has typically 110 amp hours .. two of those in parallel give ya 12V and 220 amp hours..
But the catch is that a GC2 6V or T105 size 6V is much closer to a group 24 in foot print, than a group 31 is, with the one exception being height.
Foot print to foot print the group 24 is closest to a 6V so the Ah bang for the foot print size is pretty big. A single group 24 is roughly 75Ah two is 150Ah. 2 6v batts are 225 Ah.. So for the same foot print of two 6V batteries you'd need three group 24 batteries to get your 225 Ah's. Losing one whole battery is a lot of space savings. Sadly many boats have battery boxes that will only fit two group 24's and even the 2.75" longer group 27's won't fit so two 6V batts can often give you the Ah you desire so long as you can accommodate the taller 6V height of roughly 1".
The real benefit however comes from the significantly thicker plates in the 6V batteries leading to longer cycle life. They only need to pack three cells into a 6V box vs. the six cells in a 12V box. If our boat could fit four 6V batts, plus a reserve battery, without major surgery, I'd go back to them in a heart beat. Sadly I only have space for 3 group 31's...
Not necessarily a good idea unless you can get four in there, as you have no redundancy. If you have only 2 - 6V batteries and one fails, you have no power. With 2 - 12V batteries, you can accommodate a failure of one battery.
Larry
Larry
This is why most boats have a reserve/start bank as well as a house bank. I would agree if they are the only batteries on the boat though that two 12V make more sense..
In all my years working on boats I have seen perhaps one person correctly diagnose a bad battery out of a bank while out at sea or off cruising and remove it from the mix. With newer technologies like GEL and AGM this is made even more difficult without the ability to do an SG test as the OCV often looks fine, even when you have a bad battery.
6V batteries are also far more robustly built and will take a lot more abuse than their 12V counterparts will so it has been a very, very rare occurrence that I have seen a bad cell or bad battery out of a combined 6V bank than I have with 12V batteries.
Had a set of AGM batts just last week and OCV was fine but the bank was not holding a charge. One battery was okay to marginal and the other was near toast but still put up 12.6-12.7 volts, same as the other one. A 500A carbon pile load test backed up by a test with a $750.00 analyzer confirmed which was the really bad battery and which was the marginally bad battery. The windlass could have confirmed this had the owner known how to test it and what to look for.
I personally have no worries at all with 6V banks that only have two batteries so long as the system was designed correctly from the start and that would include a reserve battery.
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