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Old 03-19-2016, 06:33 AM   #31
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DR, your last sentence... I overheard the lady I worked with in a conversation; she had another battery failure... second one in about 5 years. I had to think, but realized that my 2002 Chevy still had the original Delco battery (this happened in 2009), so I mentioned that fact. You know the very next morning, my truck wouldn't start... dead cell. I know this was coincidence, but amazing none the less.

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Old 03-19-2016, 10:36 AM   #32
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Originally Posted by pmsherman View Post
I've seen this argument of using two 12V in parallel vs two 6V in series and question the wisdom of the statement "if one 12V goes bad, you still have the other one."

From a technical standpoint that statement is true but from a practical standpoint, it may not be. If one of a pair of 12V batteries fails in service, it will probably have a shorted cell (maybe more than one shorted cell) caused by deposit buildup on the bottom of the battery. Once this happens, the bad battery will immediately discharge the remaining good battery and you'll end up with one shot battery and one fully discharged battery. If you don't figure out which one is bad and recharge the remaining good one within a few hours, keeping it in its discharged state will most likely permanently damage the good battery.

Assuming you've saved the good battery, it's probably as old as the failed one. Do you want to replace one battery and have a new one and an old one in parallel? I wouldn't want to do that.

12V deep cycle batteries in the $100 price range are almost always "marine" batteries that are hybrids, not true starting batteries and not true deep cycle batteries. 6V golf cart batteries are solid plate units, true deep cycle batteries, much more capable of surviving discharges to less than 50% of capacity than hybrids. The don't have the CCA rating of hybrids or auto starting batteries but are designed to survive sustained lower current drains to a deeper discharged state.

The reserve capacity of a hybrid marine battery is determined by draining it with a 25A load. Golf cart batteries reserve capacity is determined using a 75A load. When comparing batteries, don't forget to account for this difference in testing procedures.

Replacement wet cell lead acid batteries are available from big box and auto parts stores all over the country. I'd have no concern about two 6V series connected batteries being less reliable than two 12V ones in parallel. If one fails in either case, both will probably be replaced and if I'm travelling, it'll probably be less than two hours travel from where I am.

I also carry a 12V 100AH battery for hobby use. This could be used as an emergency replacement for the house batteries in my Georgetown if absolutely necessary.


There is a lot of truth in what you have written.

It is just the basic statement "if one 12V goes bad, you still have the other one." That gets to me. I guess I am just nit picking. I picked up a few screws a while back in on of my truck tires. They destroyed that tire. It was less than a year old but I guess I should have replaced all the tires because it was going to happen to all of them. Anything is possible.

When I need to replace my batteries I will probably go with four 6 volt gc batteries. I will run one pair and when they get low switch to the other pair. With the load I have they should last me "forever". For now I am running a 12 volt deep cycle and a 12 volt agm battery. This is only because this is what I had available. So far no problems but not what I would recommend, LOL!

Now which one is going to go bad next weekend?


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Old 03-22-2016, 10:43 PM   #33
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I added a second group 24 12v at purchase. I'm pretty happy with that.

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Old 03-23-2016, 03:54 AM   #34
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Originally Posted by Manion View Post
I added a second group 24 12v at purchase. I'm pretty happy with that.

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Old 03-23-2016, 06:14 AM   #35
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Originally Posted by Manion View Post
I added a second group 24 12v at purchase. I'm pretty happy with that.

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I've been using two 12v deep cycle batteries for almost 10 years now and along with my Honda 2000i and a 400w inverter, we have had no problems dry camping.
If not for clearance issues, I'd have two 6v golf cart batteries.
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Old 03-23-2016, 11:34 AM   #36
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Originally Posted by dragon-roo View Post
No... you would never want to mix the pair of sixes in parallel with the single 12v for more than a few minutes. You could swap back and forth between the two, but different capacity batteries in parallel will see one being a parasite of the other and almost always ruins at least one of the batteries.

Even with two 12v batteries in parallel you want to stick with same size batteries. Some even go so far as to say you need batteries from the same batch, but 'my' real world experience so far has been that you don't need to get THAT crazy.
I concur. Mismatched sets will run you down to the performance of the lowest, weakest battery. A bad cell in one 6 volt may leave you stuck, but a bad cell in one 12 volt in parallel with the other 12 volt will likely have killed both 12 volts before you catch it. In our F-250 diesel one of two batteries went bad. FORD authorized replacement of both for the above reasoning since starting voltage is critical to our electronic starting system.
Even when we ran the third Group 24 sized battery in the TH, it was newer and different from the two mains, so I segregated it by a switch, so that it did not charge and discharge repeatedly with the two main batteries. WE kept it in reserve IN CASE we ran things down too far dry camping. The blessing is that our basic 200 watt solar panels and PWM charger that someone referred to as a trickle charger keep the two mains at a safe usable level in almost every case, without having to think about it at all. So I would say, not to worry about a PERFECT solar charging system, but get 100 watts or more on the roof so you never even have to worry about the batteries in storage and almost never have to think about them while camping.
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Old 03-24-2016, 10:38 AM   #37
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One thing never to go cheap on and it has its value in an RV and vehicle is a good battery changed every 5 years.

Also maintenance or constantly monitoring it pays off plain and simple

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