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Regular
Location: Santa Cruz, Calif. | Since this forum needs a little boost, lets talk about coach (sometimes called 'domestic') batteries. There has been an ongoing argument in the rags and amoung RVers about what is better, two 6V batteries (sometimes called 'golf cart batteries') wired in series to make 12V or two 12V batteries wired in parallel. What bothers me about these arguments is that no one looks at the numbers. They just swear that they've gotten better service out of one configuration or the other. There's arguments for both, but there is a 3rd better solution.
But first, lets talk about the two 6s or two 12s.
Using two 6 volt Deep-Cycle batteries hooked up in series is a good solution; but it tends to be a bit expensive. There is a common misconception that two 6-volt 200 amp-hour batteries used in series will double the amp-hours available. This is not true. It will double the available power (watts) but not the amps. In other words, they will drive more gear, but not longer.
Remember back in your high-school science class the formula W = V*A? That's Watts = Volts * Amps. One 6-volt battery times 200 amp-hour = 1200 watt-hours, times 2 batteries = 2400 watt-hours. One 12-volt, 200 amp-hour battery = 2400 watt-hours. Each setup will deliver the same amp-hours and wattage given the stated ratings.
Using two 12 volt Deep-Cycle batteries hooked up in parallel will also work as long as the batteries remain a matched pair. In this case you will get the total amp-hours of both batteries. For example: 12 volts times 130 amp-hours = 1560 times 2 = 3120 watt-hours. The problem is that as they grow older and one battery becomes slightly weaker, it will draw down the other battery even with no external load from the camper. This constant load will cause one or both to fail much faster than they might under a normal load. Series batteries don't do this. A standard battery isolator won't solve the problem because both batteries share the same load. Someone could design one, but I don't think it is worth the effort.
So, contrary to the myth, two smaller 12 volt, 130 amp-hour batteries will deliver more power than two larger 6 volt, 200 amp-hour batteries.
My preference (the 3rd possibility) is to install the largest single 12 volt Deep-Cycle battery I can find. These are available at truck stops, not the corner auto store or Costco. One with the most amp-hours, that will fit in the available space. It will cost less than either of the other solutions, deliver about the same power and will probably last longer than two 12 volt batteries in parallel.
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Veteran
Location: Canton, (Sixes) GA | This summer before the rallies, I installed two Trojan T-105's (6V, 220 amp hour) for $200.00. I feel comfortable with my decision and planning to do more and more dry camping. Learning to control the draw is important in any solution.. Your numbers make sense, but two trojan's is a solid reliable solution for many RV'ers and boaters. Depends on your style of camping - if just moving from one campground to another with shore power, you don't need much house battery. An updated modern converter/charger is a worthwhile investment. And perhaps an inverter.. Denny | |
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Veteran
Location: Canton, (Sixes) GA | Perhaps of more value for discussion regardless of the choise of batteries, is proper battery care. There is a lot of information available. One site I have pretty much memorized is http://www.ccis.com/home/mnemeth/12volt/12volt.htm I keep my coach at home and it stays on shore power. I unplug the converter and just run it a couple of days a month. This keeps the batteries from boiling dry. My engine alternator will provide 14.4 volts whenever I run the coach, and occasionally I high charge at 15.5. There are many basic practices that are invaluable.. Folks with solar systems are well versed on battery maintenance procedures that can be helpful on coach batteries. ..Denny | |
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Regular
Location: Clovis, Ca | I use T105 6v's
Good experience.
Also, if you have series connected, 12v, you will have one cell for every two volts. If one cell goes, you will drop to 10 volts. Replacing one battery will solve the problem.
If you run two 12v batteries in parallel and one cell of one battery goes down, it will "drag" the other battery down with it, producing a load on the good battery that could damage it, potentially making it necessary to replace both batteries.
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6+6 or 12V batteries