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Old 09-29-2011, 09:53 PM   #1
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Noob battery questions

It is my understanding that 2 six volt batteries are better than 1 twelve volt battery , is that correct? When you hook up 2 6V batteries that are for example 100 ah , would I have 100 ah at 12V or 200 ah at 12V. Thanks.
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Old 09-29-2011, 10:00 PM   #2
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Too many variables. What you get with two 6VDC golf cart batteries is longer run times. What you make in essence is one very large 12VDc battery when you put two 6 volts together.
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Old 09-29-2011, 11:04 PM   #3
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So I would have 12V at 200ah's using that example ?
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Old 09-29-2011, 11:11 PM   #4
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Yes
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Old 09-29-2011, 11:21 PM   #5
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Incorrect. You will have 12volts and 100Ah capacity. When you connect in series the voltages are additive and the current capacity remains the same. When you connect in parallel the voltage remains the same and the current capacity is additive.

Examples using 100Ah/6 volt batteries:
Ten batteries in series = 100Ah at 60 volts
Ten batteries in parallel = 1000Ah at 6 volts.
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Old 09-30-2011, 12:34 AM   #6
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Jim is correct. For further proof, I refer you to the 12V side of life.
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Old 09-30-2011, 05:46 AM   #7
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jim is correct. and cut in half again to get usable amps. 50 amp hr then recharge for long batt. life.
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Old 09-30-2011, 06:28 PM   #8
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Make it easy and use the right units for energy and power.

You have about 12 usable watt hours of energy per pound of battery. This is to the 50% discharge point (optimum cost effective life cycle depth) and applies to all lead acid batteries. Figure that number varies up to about 10% depending upon battery, age, temperature, use profile or whatnot.

one battery is about 60# so that's 720 usable watt hours of energy storage.

two batteries is 2*60# so that's double the energy storage.

Whether you use 6v or 12v in your battery bank is not an issue except for how they get wired to provide the proper house voltage.

Note that watts is amps times volts.

Note that typical household energy use is about 30 to 60 kWh/day. Your RV battery bank at 1 or 2 kwH energy storage should last for for 2 or three days. What that means is that adding batteries doesn't do much; you need to adjust your RV lifestyle to deal with the small amount of energy storage.

I think I need to keep score on how many of these threads someone comes in with the 12v manual as if it answers all questions. It's often way too much making it difficult to find what is needed.
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Old 09-30-2011, 11:02 PM   #9
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Quote:
Originally Posted by Kurmudgeon View Post
Incorrect. You will have 12volts and 100Ah capacity. When you connect in series the voltages are additive and the current capacity remains the same. When you connect in parallel the voltage remains the same and the current capacity is additive.

Examples using 100Ah/6 volt batteries:
Ten batteries in series = 100Ah at 60 volts
Ten batteries in parallel = 1000Ah at 6 volts.
So then what is the advantage to running 6 volt batteries? Wouldnt that just double the weight for the same amount of amp hours you could have if you just started with a 12V battery?
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Old 09-30-2011, 11:47 PM   #10
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Because the cells are physically larger the AH rating of 6 volt batteries is about double the AH of 12 v batteries - compared to 12 volt batteries of similar size.

So two 400 AH 6 volt batteries will give you 400 Ah at 12 V.

A single 12 volt battery will yield 200 AH at 12v.
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Old 10-01-2011, 05:06 PM   #11
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It is not the fact that the batteries are 6v or 12v. The batteries we are talking about, type GC2, are a heavy duty deep cycle design used primarily in golf carts. They happen to be 6v batteries (golf cart batteries also come in 8v), but their value is that they give excellent performance and longevity in a RVs as well as golf carts. There are also some excellent 12v deep cycles, e.g. the Trojan 27TMH or Trojan 30XHS, but they are quite pricey. Most lower-priced 12v batteries are not designed for deep-cycle applications, or may be a hybrid of starting and deep cycle characteristics, so they don't hold up as well in RV use. Golf cart batteries are a higher volume production item so they are priced lower due to the economy of scale, so you get a excellent price/performance ratio.

So, a pair of GC2 6v batteries in series makes a big 12v battery with about 225 amp-hours of capacity. You could put two Trojan 27TMX in parallel and get 230 AH, but it would probably cost you 50% more for the same battery life. Or go to Walmart and get two 12v group 27 trolling motor batteries at a reasonable price and get about 210 AH but a shorter useful life, maybe 3 years instead of 7+.
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Old 10-01-2011, 06:38 PM   #12
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I dont know why people still cling to the "fact" that 6v is better than 12v... It depends on the math, battery type, battery quality and your usage.
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Old 10-01-2011, 08:17 PM   #13
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I don't know the technical reasons but I have used two 6v GC-2 batteries on my TT for years. I could get 7 days of dry camping use easily with reasonable use of lights, ect. Compared to 2 or 3 with one 12v deep cycle. It's no contest.

We just traded our TT for a 2001 Winebago class a that has 2 12's for the house. I kept the 6's and plan to swap them for the 12's.
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Old 10-02-2011, 05:33 AM   #14
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Quote:
Originally Posted by Yellowreef View Post
I dont know why people still cling to the "fact" that 6v is better than 12v... It depends on the math, battery type, battery quality and your usage.
If 6V isn't better than 12V, maybe you should tell us why. Inquiring minds want to know.
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