# Converting To Dual 6 Volt Batteries



## GoVols (Oct 7, 2005)

I have found a place locally to get Trojan T-105 batteries for $88 each. My questions are: 1) What gauge wire do I need for the series connection?, 2) Are the stock positive and negative leads OK to use?, 3) Do I need to add anything else?


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## CamperAndy (Aug 26, 2004)

The stock pos/neg wires are fine. As for what goes between you just need to be at least as big as the stock wire.


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## PDX_Doug (Nov 16, 2004)

JT,

You can use the same wire you have now. No need to go to a bigger gauge. If you currently have dual 12V's, then you should have everything you need. Just be sure to wire them in series... not parallel as they are now!

Happy Trails,
Doug


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## GoVols (Oct 7, 2005)

Right now I have a single group 24 12v Interstate battery. I plan on going dry camping later this fall for 4-5 days and we will likely be using the furnace at night. Instead of just buying a second grp24 12V battery to run in parallel or switch, I'm thinking of going to the Trojans. A set of Trojans will give me at least twice the amp hours than a set of two 12V batteries will provide. I will need to get a series cable to connect the batteries together.


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## California Jim (Dec 11, 2003)

I found that the factory wires jumping my old 12v's were too small, and even the factory ground that ran to the frame was marginal too.

You can upgrade the wire guages by picking up some "terminal to terminal" battery cables at your auto parts store. They're a typical automotive heavy guage (can't remember #), and have the terminal ends crimped on and are ready to go. No fab needed, just buy the correct length. I used them for crossover cables and also replaced the factory ground to the frame.

Now the factory hot wire is the weakest link, but it's still acceptable.


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## NJMikeC (Mar 29, 2006)

Jim,

I'm kind of with you , stock wires look skimpy, but the fact is the current draw doesn't really necessitate the change. Think we are all used to looking @ 2 and 4 guages on the car. They are needed there. Current pull is 100AMPS.


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## Insomniak (Jul 7, 2006)

GoVols said:


> Jim,
> 
> I'm kind of with you , stock wires look skimpy, but the fact is the current draw doesn't really necessitate the change. Think we are all used to looking @ 2 and 4 guages on the car. They are needed there. Current pull is 100AMPS.


If you're going to use an inverter, the wires between the batteries definitely needs to be upgraded. Even a 1000 watt inverter can pull 150 amps when it's surging. Since the batteries are so close, the wire can be a bit smaller, but still use #2 or #4 wire.


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## GoVols (Oct 7, 2005)

Insomniak said:


> Not really GoVols. When you wire two 6 volt batteries in series, you double the voltage but not the number of amp-hours. For example, two 12 volt group 24 batteries with 85 amp-hours each wired in parallel will give you 12 volts and 170 amp-hours. Two six volt Trojans with 220 amp-hours each wired in series will give you 12 volts and 220 amp-hours. Still, a 30% increase, but you'd be hard pressed to double the amp-hours with just two batteries.


I have discovered that there are many ways to slice the battery comparisons. Unfortunately, I can't find where Interstate posts a 20 hr. rate (industry standard) for their batteries like Trojan does to make a direct comparison. What I can compare is Hours @ Amp Load. An Interstate SRM-24 will provide 138 minutes at 25A; a set of T-105's will provide 488 minutes @ 25A. This seems to be a 253% increase over a single 12V and a 76% increase over 2 12V batteries wired in parallel. I don't know how this reconciles with your 30% increase assertion above. Am I missing something?

Also, the T-105's are built strictly for deep cycle; the Interstate RV/Marine battery is not.


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## Insomniak (Jul 7, 2006)

GoVols said:


> Not really GoVols. When you wire two 6 volt batteries in series, you double the voltage but not the number of amp-hours. For example, two 12 volt group 24 batteries with 85 amp-hours each wired in parallel will give you 12 volts and 170 amp-hours. Two six volt Trojans with 220 amp-hours each wired in series will give you 12 volts and 220 amp-hours. Still, a 30% increase, but you'd be hard pressed to double the amp-hours with just two batteries.


I have discovered that there are many ways to slice the battery comparisons. Unfortunately, I can't find where Interstate posts a 20 hr. rate (industry standard) for their batteries like Trojan does to make a direct comparison. What I can compare is Hours @ Amp Load. An Interstate SRM-24 will provide 138 minutes at 25A; a set of T-105's will provide 488 minutes @ 25A. This seems to be a 253% increase over a single 12V and a 76% increase over 2 12V batteries wired in parallel. I don't know how this reconciles with your 30% increase assertion above. Am I missing something?

Also, the T-105's are built strictly for deep cycle; the Interstate RV/Marine battery is not.
[/quote]
Are you comparing one group 24 battery to two Trojans? To compare apples to apples, you would have two group 24 batteries providing 276 minutes at 25 amps - remember, you double the amp-hours when paralleling 12 volt batteries. This would give a difference of a little more than 40%. In the real world, I can tell you, you won't see a huge amount of difference between the two. Yes, the Trojans are built to be a deep cycle battery, but so are the Interstate and a lot of other brands, unless they're a hybrid. I know people who have been running 12 volt batteries, properly maintained for more than 5 years.

If you want to see multiple threads about the argument between the two, go to rv.net and you'll get multiple pages of comparisons.

Let me add on edit, that an increase of 30-40% in capacity is still a respectable amount! The other big considerations would be the increased cost, slightly bigger size, and weight of the Trojans. Also, if one of the 6 volt batteries craps out, you're dead in the water. If one 12 volt battery dies, you still have one as a backup!


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## GoVols (Oct 7, 2005)

Insomniak said:


> Also, if one of the 6 volt batteries craps out, you're dead in the water. If one 12 volt battery dies, you still have one as a backup!


Oh yeah; didn't think about that. Maybe a group 29 or 31 would be better and have two switched 12V batteries instead.

No, wait a minute . . . the battery trays will only hold a group 24 length battery . . . or a T-105 six volt.


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## Insomniak (Jul 7, 2006)

GoVols said:


> Also, if one of the 6 volt batteries craps out, you're dead in the water. If one 12 volt battery dies, you still have one as a backup!


Oh yeah; didn't think about that. Maybe a group 29 or 31 would be better and have two switched 12V batteries instead.

No, wait a minute . . . the battery trays will only hold a group 24 length battery . . . or a T-105 six volt.
[/quote]
I wouldn't totally discount the Trojans - a lot of people use them and are very happy. Just when you add up the pro's and con's, the advantage doesn't seem so obvious. I don't think they go bad very often, but it is one thing to consider.

Somebody around here (I think) did a mod where they added wood to the bottom of the battery trays, making them flush with the frame. That allowed them to put in two group 27 batteries. That combo would give somewhere around 230 amp-hours and cost a lot less than the Trojans too. I'm thinking I might go that route since I wouldn't have to worry about battery boxes if they're under the propane cover.


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## Scrib (Jun 28, 2005)

Insomniak said:


> That combo would give somewhere around 230 amp-hours and cost a lot less than the Trojans too.


They were both about $70 when I was shopping around.


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## PDX_Doug (Nov 16, 2004)

I was reading an interesting article in the current Road & Track about the new hybrid cars. It seems Toyota has been studying battery life in thier hybrids for several years now (since they went on sale in Japan in 1997), and have found the greatest chemical stress on any battery occurs at its operational extremes, the last 20% before full discharge, and the top 20% of full charge.

As such, they now control the batteries in their current hybrids to run in the rather narrow 50 to 70% charge range. Bottom line, deep cycle battery or not, you will get the best longevity if you avoid deep discharges, and total capacity recharges.









Happy Trails,
Doug


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## Huskytracks (Apr 18, 2005)

Just wanted to add my .02. Just run ajumper from the pos of one batt to the neg of the other and hook up the trailer leads to the other pos and neg. 2 guage should do the job and will cost about the same as anything smaller.


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