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Old 03-09-2015, 07:55 AM   #1
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Totally confused on batteries

I bought an older class a with 2 12 volt batteries for house batteries. They are actually cranking batteries. They are old and worn, work but discharge quickly and one cell in each is dead so have to be replaced.

I have read a hundred posts here and do not really know if i should replace with two 6 volt high amp batteries or 2 12 volt AGM.

I would appreciate it if someone could steer me straight on this matter. My brain tells me 2 12's are better than 1 12 but hell i am no electrical engineer.


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Old 03-09-2015, 08:09 AM   #2
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Boy did you open a can of worms. First thing is to ensure we are actually talking house and not engine cranking/starting bats. Generally speaking, 6-volts in series are better for repetative, deep-cycle [50%] recharging house batteries. Deep cycle 12v bats and AGMs will be fine too but you pay dearly for AGMs. The best explanation--perhaps not very scientific--is to go by weight [eg more lead, more amp hours]. As long as they are deep-cycle, one big 12v, two avg 12v, two 6-volts or AGMs, they all work.
PS--in keeping with the weight theme, and assuming you have an inverter for 120v capability, one or two batteries of any kind wont give you a lot of capacity--four or six, 6-volts bats, for a Class A is pretty std.

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Old 03-09-2015, 08:09 AM   #3
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Two 6 volt are better than two 12 volt,, I know but thats what "they" say.. Google "The twelve volt side of life" for some light reading,, they explain it.. Most recommend going to Costco for the Golf cart batteries.
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Old 03-09-2015, 08:11 AM   #4
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Unless money is an overriding concern, I highly recommend you go with AGMs. Excellent reliability and zero maintenance. Lifeline's are the best, any other AGM is a step down but will still be better than wet cells. 12V vs 6v doesn't really matter (if you go with 6v you'll just wire them to deliver 12v) but it will be easier to just replace your two 12v batteries with 2 12v AGM replacements.
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Old 03-09-2015, 08:12 AM   #5
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Two six volts are better than two twelve volts. The question is, how do you camp. If you stay at campgrounds every time. My advice is to use just one twelve volt. It reduces weight and cost. If you dry camp and stay at WalMart a lot then go with two six volts. Twelve volt batteries have a lot of thin plates. this is to give a lot of amps for a short period of time. (starting the engine) Six volt batteries have thicker plates and are made for long discharge periods. Six volts are designed to be deep discharged.
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Old 03-09-2015, 08:13 AM   #6
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yes they are the house batteries. What were in there were two 12 volt cranking batteries 4 years old that had run their course. I don't know how heavy but taking a guess i would say maybe 40 lbs.

MY point here is i am confused as to whether I should just swap out the 12's for better 12's, say two atrong AGM's or go with two 6's with 220 amps each
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Old 03-09-2015, 08:19 AM   #7
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The voltage has nothing to do with it - it's the battery type and size/capacity that is important. And cost, of course. The "6v" that RVers refer to is the GC2 "golf cart" battery and they yield about 230 Amp-Hours per pair and typically cost around $120 each. A pair of 12v deep cycles in size Group 29 or 31 will deliver about the same amp-hours but typically cost much more, maybe $170-$200 each. GC2 batteries are produced and sold in high volume, so the pricing is usually better than the 12v deep cycles (which are a low volume specialty item).

AGM technology is excellent for a deep cycle battery but it's main advantage is low maintenance. It actually has a bit lower amp-hour capacity than a flooded cell deep cycle. And the price premium is usually substantial. However, if you are the type that forgets to maintain your flooded cell batteries, the extra up-front cost of an AM may pay off in the long term with extended battery life. The flooded cell will die of neglect while the AGM keeps on going.

I've written an article on Choosing the Right Battery for Your RV - it is available HERE.
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Old 03-09-2015, 08:21 AM   #8
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What battery(s) you select will depend a great deal on how you use the MH, particularly what loads you place on the 12 volt systems. And of course your pocket book.

We do a great deal of boondocking and would probably be better candidates for AGM type batteries, but we opted to simply visit Walmart and buy a marine, deep cycle battery.

Regardless of which direction you go, I would pay attention to 12 volt "Phantom Loads". These are things like radios, TVs, clocks, etc that drain a small amount from the battery, even when they are turned off. These can run a standard battery dead in a few weeks.

I installed a "Phantom Load" switch so I can completely remove power from these devices.

Phantom 12 volt Loads | 2001 Coachmen Mirada 300QB
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It won't do MACH 2, but I can get a sandwich and take a pee.
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Old 03-09-2015, 08:38 AM   #9
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There are two ways to look at batteries: the complex, techie, engineering-design driven view and, my point of view, the happy user perspective.

First, my recommendation. Install two good quality, deep cycle, 6V lead acid batteries such as the Trojan T105. A little more pricey but lasts a long time and provides a 10hr rate of 207AH, enough power for most needs.

I'm a happy user and rarely give my batteries any thought except to check water every 3 months. In my previous 24' WGO Class C, I ran T-105 that lasted nearly 7 years. In our current WGO 30' Class A, I installed two Trojan T-145 for a 10-hr rate of 239AH.

If you want the best, absolutely no maintenance solution and you're not cheap like me, go for a pair of AGM batteries that offer the highest AH rating and will fit in your battery compartment.

Bottom line, don't worry about 12v vs 6v, lead-acid vs AGM, yada, yada. Go with what a happy user recommends. Batteries aren't rocket science. (Full disclosure - I mostly boondock and rarely hookup so my battery needs may be different that yours.)

In any case, be sure you have a good 3 or 4 stage converter to prolong battery life. I installed a PDI4645 in both rigs. Down here in the Southwest, a solar system is a no-brainer. My batteries are fully charged by 10AM most mornings. If it's cloudy and overcast, it might take most of the day. HTH.
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Old 03-09-2015, 08:34 PM   #10
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I tend to agree with LeeOts I've had both 12's and 6's and I much prefer the 6's and I'm cheap as well and went with 6V Lead Acids.

I also boondock often sometimes for 10 days or more at a time. The maintenance on a lead acid is pretty minimal as long as you do it and the price difference for the AGM's just wasn't worth it to me.

If possible, check a local RV show, the often have pretty decent deals.

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Old 03-09-2015, 08:54 PM   #11
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The two things to consider is how do you camp if you need some boondock capacity to stay in walmart over night then you will need more amp hours.

The second thing is space. you can get 2 golf cart 6 volt batteries and wire them in parralel but you find that most MH that have the 6 volt have at least 4 and if a newer all electric they have 6. If you only have space for 2 batteries then get the 12volt trojan deep cycle batteries. 2 of them will give you almost the same amp hours as 4 of the golf cart 6 batteries. Of course they will be pricey as mentioned above but it will give you the same amp hour capacity as my (4) 6 volt batteries.
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Old 03-09-2015, 09:20 PM   #12
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I see a lot of interesting conflicting information but no one mentioned the killer issue. Most C's have their batteries frame mounted probably under the step. Measure the size you have now and measure any extra space you might have. Then you can go to any site like this one for Trojan:


Look at the size batteries that will fit and the terminal type you need to match what you have. That will tell you your options. In general the heavier the battery that will fit in your space the more deep cycle capacity it will have so the longer it will last. The best choice is the biggest one that will fit safely. The next best is the next size down. Sometimes the second best is significantly cheaper because the manufacturing runs are bigger. That is the deal with the golf cart batteries. If you get this far and get the dimensions then post again and you will get more help. ;-)
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Old 03-09-2015, 09:27 PM   #13
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On the six-twelve question, the only real difference is how the space is divided up in the battery itself. For the exact same physical space the 12v battery will consist of 6 compartments with lead and separators, with each compartment filled with a sulfuric acid solution. Each compartment is separate from the others.

The 6v battery is the same except that there are only three compartments. Having fewer compartments requires less separator material. That's the major difference; more of the volume is devoted to the lead/acid, and less to separator material, therefore the electrical capacity is slightly greater in the six volt battery. Put two six volt batteries in series and you get slightly more AH capability than the same size and weight of twelve batteries.

Other than that, no big deal. Big equipment such as bulldozers often use BIG twelve batteries. They come out to about the same size and weight as six volt pairs. Big difference is that the six volt batteries are easier to carry.

TMI ? Yeah, probably so.

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Old 03-09-2015, 09:28 PM   #14
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Without breaking the bank flooded 6V GC2 batteries which are True Thick Plate Deep Cycle properly taken care of will last you 5 + years easy. Compare dollar to Amp Hour rating you will be money ahead with the flooded GC2 6V. If you're concerned with maintaining the electrolyte level get a Flowrite Battery Watering System. Makes it very simple to check the batteries cell level, just takes a few minutes to know their full. Marine deep cycle are no better then normal automotive starting batteries. Either way you go AGM or flooded you should upgrade the charger to a 3 or 4 stage charger. Especially if you go with AGM.

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