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Old 09-07-2010, 12:39 PM   #1
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Two 6-volt vs. one 12-volt battery

I have two 6-volt batteries currently installed in my coach but I’ve noticed that both batteries need to be replaced. I’m wondering what the advantage is to having two 6-volt batteries vs. having just the one deep cell 12-volt battery.

I also want to mention that I have solar charger installed and the batteries will be installed into a 98 Winnebago Adventure.
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Old 09-07-2010, 02:07 PM   #2
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The capacity you have available is primarily about weight and that means size. The voltage of batteries in a bank or their brand or whatever are of minor concern in RV sized battery banks. Figure about 10 - 15 usable watt hours per pound of battery in your bank. Sometimes having a couple of 60 pound batteries rather than one 120 pound battery can be more convenient.

Don't get caught in the 'true deep cycle 6v golf cart' myths. There really isn't any such thing as a 'true deep cycle' when it comes to batteries available for an RV and the only concern about voltage is to make sure the wiring is right so you have proper bank voltage for your rig.

Get batteries from a retailer who sells a lot to folks like you, offers a good warranty and will stand behind what he sells.

What makes the difference in RV batteries is your use and maintenance. Put your effort and money into good charging and good maintenance equipment and then take proper care of your batteries. You should get a good 5 years or more of battery life if you do.

If you have solar, at least a watt of solar panel for each pound of battery makes for a good guide.
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Old 09-07-2010, 04:18 PM   #3
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Quote:
Originally Posted by Ohsirr View Post
I have two 6-volt batteries currently installed in my coach but Iíve noticed that both batteries need to be replaced. Iím wondering what the advantage is to having two 6-volt batteries vs. having just the one deep cell 12-volt battery.

I also want to mention that I have solar charger installed and the batteries will be installed into a 98 Winnebago Adventure.
Do your 2 (two) 6 volt batteries power your coach or are they wired for engine starting? (or both?)
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Old 09-07-2010, 04:21 PM   #4
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they are wired for the coach and are used as a backup when the engine battery is dead.
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Old 09-07-2010, 06:23 PM   #5
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What is the advantage of a 2 piece 12 volt battery over a 1 piece (There are no six volt batteries in RV's only 12 volts that have been broken in 2 for easier handling, of course, outside the motor home each half is six volts)

COST. simply COST

Due to the fact that there are thousands and thousands of golf cars across the nation that use this specific battery where as with the 12 volt designs there are dozens of different batteries all of which could do the same job, but they terminals are on different or the size and shape is a bit different because ... Well, you can't just have a generic car battery now you got to have a special battery for each make and model.

Thus the cost of production is lower for the golf car batteries, Because they are more standardized.

Beyond that. You can get a starting battery in 12 volt, and a marine/deep cycle (Which is mostly a starting battery) but up till very recently finding a true DEEP CYCLE 12 volt battery in a format you could lift and install in your motor home was a real job.

I have used 12 volt deep cycle batteries in the past. .. but you needed a fork lift to pick them up (NOTE: one of them powered said fork lift)

But the big advantage is cost. check the price on the six volts at Sam's or Costco.

NOTE: That pair of golf car batteries is about 220 amp hours

In 12 volt that's about an 8D or 4D battery Check the tonnage on those puppies.
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Old 09-07-2010, 07:19 PM   #6
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re: "Thus the cost of production is lower for the golf car batteries, Because they are more standardized."

You need to fill me in on where you do your shopping! In the places I go (Costco, Sams, Walmart, specialty battery store), the 'golf cart' batteries tend to be more expensive on an available energy capacity basis.

re: "finding a true DEEP CYCLE 12 volt battery" -- there is no true deep cycle battery of any voltage that is commonly available for RV service. Anyone who does deep cycling on wet cell lead acid batteries (i.e. down 80%) is asking for a very short battery life. Also, if you take apart the batteries, you'll find they all use Faure construction and have plates of about the same thickness (0.1 plus or minus half that). The differences are minor compared to other things that will impact service satisfaction. (a more detailed analysis is available on request).

re: "Check the tonnage on those puppies" -- all wet cell batteries for RV service have about 45 wh/kg (batteryuniversity.com or check the line cards) or 10 - 15 watt hours per pound usable energy.

re: "That pair of golf car batteries is about 220 amp hours" -- one should always multiply the amp hour rating of a battery by its voltage to obtain watt hours. That way batteries of different voltages can be properly compared and it is also easier to gain a bit better understanding of just what sort of energy they will provide (compare to the typical 30,000 watt hour daily household use).

As for the standardization and manufacturing efficiency, I don't think you'll find that a factor in this realm. The reasons go from total production counts to the base use of standard parts in battery manufacture.
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Old 09-07-2010, 09:30 PM   #7
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Battery storage capacity is based primarily on the amount of lead in the battery for wet lead/acid like most of us use. The heavier the battery, the more storage available in the most basic of terms. Most 6v golf cart batteries are heavier than 12v deep cycle that we commonly use. There are exceptions to this though.
In years past I would use batteries as a source of lead for bullet casting as they were ffree to me. The 6v batteries normally had thicker and larger plates.
As a side note the majority of golf cart type vehicles use 12v, 24v, 36v, 48v in stages to power the electric motor that propels the cart. When my guys had to service or replace the batteries the digital camera was a very good friend. As they say a picture is worth a thousand words!
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Old 09-07-2010, 09:44 PM   #8
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1/2 dozen of this...6 of the other...

Forget about cost, and do not buy your chasis batteries at Walmart.

Best cost for non-car batteries will likely be the mom and pop battery supply, I recently purchased some 8D batteries to create a home shop forklift battery, they were $15.00 less expensive each than sams club and they were fresh.

The thickness of the plate matters a great deal.

The high capacity car batteries have thinner plates so more plates can be installed in a smaller space creating more capacity.

The cost is durability, these thinner plates get consumed by the process sooner.

The HD batteries have less capacity per pound, but will last longer.

Deep cycle is the vultage used to determine DEAD battery.

Normal battery is dead when per cell voltage is 1.75 volts, deep cycle is usually 1.65 or so, this diifference is very little, we set the disconnect for 1.8, it is very little difference incapacity but less stress on the battery.

Also look at the hour rating, many batteries will state amp hour rating, but all 100 amp batteries are not the same.

Some will state 100 amp hours @ 8 hour rate while others state 100 amp hours @ 20 hour rate, the 8 hour battery is a larger battery.
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Old 09-07-2010, 10:35 PM   #9
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re: "Most 6v golf cart batteries are heavier than 12v deep cycle that we commonly use." -- I suggest you take a look at the sizes available. I will agree that many RV's have a group 24 and that is quite a bit smaller than the usual 'golf cart' size (especially since you need 2 of the larger 6v's to get the right bank voltage). But a bigger battery will need a bigger box to put it in no matter which way you go. Group 31's make a nice upgrade, for instance. Often just doubling up on the group 24's works well, too.

re: "Forget about cost, and do not buy your chasis batteries at Walmart." -- why? there are only a few battery OEM's and Walmart sells a lot and stands behind their warranty. You can find the same battery elsewhere under a different private brand. Why should private brand make a difference? or do you just have something against Walmart?

re: "The thickness of the plate matters a great deal." -- It may for some applications but for those batteries available for the RV market, the differences in plate thicknesses are minimal and insignificant. (look for yourself - the NAWS FAQ cites the thicknesses I mentioned earlier, for instance)

re: "The HD batteries have less capacity per pound, but will last longer." -- what I suggest you do is to actually look at the specifications. You will find that the energy density per pound of battery for wet cell batteries commonly used or available in RV service is very consistent. (again, see cited reference or analyze a manufacturer's line card)

re: "Deep cycle is the vultage used to determine DEAD battery." -- I suggest getting a good battery dictionary to correct this one.

re: "Some will state 100 amp hours @ 8 hour rate" -- this is a good point but the batteries intended for RV service will almost always list an energy capacity at the 20 hour rate plus the 'reserve minutes' which is for a 25 amp draw. Search on 'Peukert' for more on how the available capacity depends upon the current the battery supplies. The 20 hour rate for commonly available RV batteries usually comes in at about a 60 watt draw so it makes for good comparisons.

It appears that I have stimulated the myth pounders out there. For those of you who don't have that disease, I suggest you look at the hard data and be very careful about what you read. Hard data is a specification or a warranty that the manufacturer and retailer will stand behind, something you can actually measure.

Keep in mind that factors such as temperature, battery age, how you use, charge, and maintain the battery, and other factors can each impact available battery energy by ten percent or more. What this means is that differences of 10% to 20% in things battery are not likely to be visible in any significant manner so don't get hung up on the small things.
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Old 09-07-2010, 11:49 PM   #10
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I just went through this on my coach. My 6 volt batteries finally gave up the ghost after 15 years? 1994 coach and they went out in 2009.

At the time, I was an Optima dealer. So it was natural for me to just grab a blue top and toss in there. The capacity sucked so bad that middle of the night my heat would go out because of the battery voltage dropping ever so slightly. So then I put a second one in place. Still, middle of the night I would have heat issues.

Did some checking with voltages when I would loose my heat.... I pulled those batteries and sold them on Craigslist for $250 and bought a pair of 6v golf cart batteries at Costco for $190, IIRC? Now I can boondock for days on end without loosing any heat in the middle of the night

Golf cart batteries for the win!
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Old 09-08-2010, 01:28 AM   #11
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There are different size 6v batteries just like there are different size 12v. I was at Sam's Xlub looking at them and they sell one I never saw in the carts in our fleet. It was about as tall as a group 24. Then they had the one I was familar with. Much taller than the 12v batteries and alot heavier. Can't remember the numbers anymore since I've retired 3 years ago but there is a significant difference in them. When I get time I will look on the web for specs.
I think my '87 Itasca may have enough height in the battery box to fit the larger version of the 6v. If so that is what I will install when my coach batteries go bad.
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Old 09-08-2010, 08:28 AM   #12
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What I have learned Over the past 70, years; is that batteries,size , is vary important;; However At the same leval of importance is the charging system; In our coach that has a 1500. watt inverter/75 amp charger. With equalizing moad our battries are over 10 years old. in that time I have added water 3 times, They still keep the 38' Ult warm in the snowmobile snow overnight; Life is good;;
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Old 09-08-2010, 09:15 AM   #13
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re: "My 6 volt batteries finally gave up the ghost after 15 years?" -- that's nice. but it doesn't help others much. (ever wonder why they don't offer warranties for these batteries to support long age?)

I could tell tales about the Trojan T105's that didn't last the summer or the B-Van house battery I replaced after near ten years just because, but I know that individual experiences don't clarify the issue much and can easily mislead.

If you look at the experience in the aggregate, that is, how long batteries last for most folks (re NAWS FAQ, for example), you'll find that 4 to 7 years is about how long 'golf cart' batteries last for most folks if properly used and cared for - about the same as any other RV service battery.

It should also be noted that batteries don't just drop dead. They tend to degrade over time. If someone has a lot of excess capacity, they may not notice the batteries getting old for quite a while. Other unknown variables include use profile, maintenance equipment, and temperatures.

But it is interesting how these reality checks always seem to bring in someone bragging about a battery life experience out in the 8 sigma range. One a while ago made a brag that indicated he had 300+ years of experience. That's pretty good considering most people don't live that long and lead acid battery technology is only 150 years old or so (and this is the century celebration for RV's).

Quote:
batteries,size , is vary important;; However At the same leval of importance is the charging system
This fits everything I have seen.
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Old 09-08-2010, 09:24 AM   #14
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Combining batteries in series provides you with the combined amperage of both, versus amperage of a single battery; plus a previous poster noted that the 12v has smaller plates, just more of them to provide enough for 12v battery cell population. A key thing to remember with something like this......if two 6's were not preferred over a single 12v, it would have been engineered that way as a weight saving measure.
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