6V vs 12v batteries - Fiberglass RV


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Old 08-10-2010, 04:36 PM   #1
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6V vs 12v batteries

I am ordering a new Escape 17' trailer, and need to decide which battery setup to use. I have had a scamp for years, and never found 1 12V deep cycle enough to get me through 3-4 days of dry camping in cold weather. I recently added a second 12V battery, and that works great. Escape recommends 2 6V batteries, saying they charge more quickly and hold up better over time but don't have more capacity than 1 12V. Is there any reason to install 2 6V's instead of 2 12V's?
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Old 08-10-2010, 04:54 PM   #2
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As I understand it, the 2 deep-cycle marine 6v's have way more amp-hour capacity than one 12v, just not more total voltage. We've been 5 cool nights out in our Escape 19 with the 2 6v-package on several occasions, and the charge level never went below "good". Another good battery life extender is to go with all LED lights inside. Tammy has a good source in Chiliwack for them.

Bruce
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Old 08-10-2010, 05:41 PM   #3
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I am interested in converting a 16' Scamp to use two 6V batteries, but am finding it hard to find a good place to compare capacity vs. price. Does anybody have a good suggestion on which 6V batteries to buy, what enclosure to use, and how much to expect to pay?

Do I need to replace the battery charger in the unit to do this?

Thanks,
Doug
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Old 08-10-2010, 06:25 PM   #4
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I like using Interstate 6 volt batteries. They have worked very well for me over the years.
Batteries - Interstate Batteries has every battery for every need
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Old 08-10-2010, 06:25 PM   #5
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Quote:
Originally Posted by Doug_H View Post
I am interested in converting a 16' Scamp to use two 6V batteries, but am finding it hard to find a good place to compare capacity vs. price. Does anybody have a good suggestion on which 6V batteries to buy, what enclosure to use, and how much to expect to pay?

Do I need to replace the battery charger in the unit to do this?

Thanks,
Doug

From my boating days I used 4 six volt golf cart batterys ( you can use two ) From Wall Mart. This is the most economical way that I know of.
If I recall correctly they run less than $100 each.
I am thinking you will have to fabricate a battery box for these.
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Old 08-10-2010, 06:47 PM   #6
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I've spec-ed out batteries several times, and as far as I'm aware it all comes down the to the amp hours of the battery at a given voltage. For example, if the amp hours of the 6 volt batteries are 100 amp/hr at the 20 hour rating (I'll explain the 20 amp rating a little later) and you run two of those 6 volt batteries in series, you get 12 volts, with 100 amp/hr rating. If you take a 12 volt battery with 100 amp/hr at a 20 hour rating, then its the same (not taking consideration quality differences etc). When you run two batteries in parallel you keep your voltage the same, but double your amp hours.

So for some examples, 2 x 6 volt batteries with 120 amp hours at 20 hour rating, is better than a single 12 volt battery with only 100 amp hours at a 20 hour rating. But if the 12 volt battery has say 150 or 200 amp hours, then it is superior.

As for the 20 hour rating thing. That basically means how long a battery can sustain a given voltage over the 20 hour period. For example, with a 100 ah battery, you can draw 5 amps for 20 hours until dead. You might assume that you could then draw 10 amps in 10 hours, but this is incorrect. If you draw 10 amps, the battery might drain in say only 8 hours or less etc as an example. Also, if you draw say 2.5 amps per hour, it won't drain in 40 hours, you might get more time out of it etc.

These specs are difficult to apply to real life situations, as most people don't sit down, calculate the amps they are drawing, over a specific amount of time. A water pump might only run once during an entire hour, and only for 30 seconds for example.

But what it really all comes down to is amp hours. Run two batteries in series, you double voltage, but the amp hours doesn't change (please you like batteries when running in series) and with parallel, you keep your voltage the same, but double the amp hours. That's why two 12 volt batteries in parallel is still 12 volts, but lasts twice as long etc. Many people run 4 6 volt batteries, two pairs in series (equaling 12 volts each) and then those two banks in parallel, thus doubling the amp hours.

I know, I ran on with this one, but if anyone has questions, don't hesitate to ask!
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Old 08-10-2010, 06:58 PM   #7
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This has been a discussed many times on many forums for years. The only reason I can see going to 6 volt batteries is form factor. (size and shape of mounting space) 2 6 volt batteries of the same AH (Amp Hour) rating as one 12 Battery will weigh more than the 12 volt, more case. Also another drawback is the connections. Every connection to a battery is a potential failure point. With Lead Acid batteries those connections will corrode and you'll have twice as many connections to maintain. Also the more connections the greater the inherent connection losses are.
We're talking basic physics here.
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Old 08-10-2010, 07:01 PM   #8
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Quote:
Originally Posted by Byron Kinnaman View Post
This has been a discussed many times on many forums for years. The only reason I can see going to 6 volt batteries is form factor. (size and shape of mounting space) 2 6 volt batteries of the same AH (Amp Hour) rating as one 12 Battery will weigh more than the 12 volt, more case. Also another drawback is the connections. Every connection to a battery is a potential failure point. With Lead Acid batteries those connections will corrode and you'll have twice as many connections to maintain. Also the more connections the greater the inherent connection losses are.
We're talking basic physics here.
You bring up some very important points. Its not apples to apples comparing 6v to 12v batteries, as Byron mentioned. Maybe the way they will be mounted is a concern? Or like he said, the cabling need are different. Not only that, but I forgot to mention the obvious choice, which is cost.
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Old 08-10-2010, 08:17 PM   #9
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Here is a post from elsewhere from a tech a Trojan Battery.

Quote:
The main advantage of using two 6 volt batteries connected in series is long life. They generally last about two times longer than 12 volt batteries. This is because 6 volt batteries have bigger and thicker plates that can better withstand the effects of deep cycling.

The main advantage of using two 12 volt batteries connected in parallel is backup. If one battery goes down, you will have the other battery to keep your system running. With two 6 volts, if one goes down then your entire 12 volt system is down.

In terms of capacity, if you get a couple of really good 12 volt, group 27 or higher, batteries then the runtime that you'll get out of the two systems is roughly the same.

If you need further assistance, please contact me.

Best regards,

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Technical Support Engineer
800-423-6569 Ext. 301
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Old 08-10-2010, 08:19 PM   #10
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BTW, I went with the two 6V batteries, and am extremely pleased. I have done 5 days with moderate furnace and light use, and the batteries were still nearly at full capacity.
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Old 08-10-2010, 09:10 PM   #11
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I've done some looking and a local store here has a 12v battery with 100 ah at a 100 hour rate. And they also have a 6v battery with a 150 ah at a 6 hour rate. So if we do some "guessing" on these batteries in the 20 hour rate, the 6v battery would perform better than the stated 150 ah over the 20 hour rating, because you are drawing less amps in that time. As for the 12v, you would perform worse than the 100 ah because you are drawing more power than the stated rate. In this case, the 12v battery is $299 whereas the 6v battery is $129.99 (double that for $260). So as you can see in this situation, the 6v batteries are a much better buy. This also doesn't take into consideration the quality of the battery, warranty etc. Just some basic numbers to consider.
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Old 08-11-2010, 10:01 AM   #12
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Quote:
Originally Posted by Doug_H View Post
I am interested in converting a 16' Scamp to use two 6V batteries, but am finding it hard to find a good place to compare capacity vs. price. Does anybody have a good suggestion on which 6V batteries to buy, what enclosure to use, and how much to expect to pay?

Do I need to replace the battery charger in the unit to do this?

Thanks,
Doug
The problem is there are many different capacity 12v as well as 6v batteries. Without manufacturer & model numbers it is difficult to compare. The big difference is between "Deep Cycle" & auto starter batteries. The deep cycle battery will handle deeper discharges as well as more charge/discharge cycles than starter batteries. Most 6v batteries are deep cycle while most 12 volt are auto starter batteries.

As to charging, since the 6v batteries are connected in series, they can be treated as a "2 part" 12v battery. You do not need to change your charger or converter as long as you connect it to the 12 volt output of the pair of batteries.

Lots of good battery info at Phrannie's Poop Sheets, Item 5.
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Old 08-11-2010, 10:39 AM   #13
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I agree with Byron. Unless there is extreme usage, such as a CPAP or other majorly required 12v draws, I prefer a single 12 for all the reasons stated.

The key is to not require so much current in the first place. Low draw, low aH requirement, light weight, less connections to fail.

I just bought a new to me trailer without any 12v system installed at all. It did at one time, but all has been removed by a previous owner. Todays project is to get started on the system.. and I am installing at the front end, a wally world group 29. I had one in the big burro and was extremely pleased at the weight and performance with just a solar charge.

OTOH.. I have 2 6s in the motorhome. With all the huge systems in it, its almost required. Everything is so power hungry that the added capacity of the 6s is a must.

With trailers "egg" sized, and all the smaller system requirements.. I prefer not to go with the extra weight and expense.
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