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Old 01-28-2007, 10:00 PM   #1
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Talking What is difference between 1 & 2 Battery systems?

Dear lovely people,


I am the proud Owner of a 68 Airstream Sovereign, and it is on a single battery 12v system.. I have seen that there are two battery 12v is there any significant advantage to this system? Any things I should know about the univolt system.
Also I am interested in Being able to Boondocking and to run the ac when I need it. I am looking for A quiet light weight generator that will work..
Thanks for the answers in advance.

David & Ann Johnson
Savannah GA

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Old 01-28-2007, 10:13 PM   #2
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There are no differences in two batteries and one battery systems. Two batteries just last twice as long when out boondocking.

Light weight generators are out there, but light weight generators and air conditioners are mutually exclusive. Both Yamaha and Honda make generators in the under 50 pound range, but generators of this size (1000 and 2000 KW) will not run your air conditioner. For that, you would need two 2000 watt generators tied together with a special harness or a generator in the 3600 KW range. Those 3600 KW's usually weigh in the neighborhood of 150 pounds. There just aren't any light weight generators that will run a 13,500 BTU or 15,000BTU air conditioner.
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Old 01-28-2007, 11:16 PM   #3
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Hi, my opinion is that two batteries will last about four times as long as one. I was in the tool business [MAC TOOLS] for eight years. My truck was built with one truck battery and one house battery. The house battery would not make it through the day, of business, without going dead. I modified the battery box and put two house batteries in it. Huge difference. Unlike an RV, this truck was out all day five days a week. The way I explain the two battery system versus one battery is; I want you to pick up a 100# barbel and start walking with it. See how far you can go. Now have a friend hold one end of the 100# barbel and you hold the other end. Now start walking with it. I'll bet the two of you can go ten times the distance than you did alone. It is just plain easier for two to hold the load than one. That's my opinion, and I'm sticking to it!
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Old 01-29-2007, 12:07 AM   #4
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David and Ann,
Two 12 volt batteries in parallel will double your power or simply translated; increase your boondocking time by 100%, no more. I loved Bob's analogy but the fact is amp hours is amp hours and it might seem like you get eternity out of a second battery but you only get twice as much, assuming they are the same size and capacity.
GStevens hit the number on the head with 3600 watts. That is the minimum you should have to run a roof mounted AC. Which generator is lightest or however you get that is your question I know but you will have to decide if you can lift such a unit or get two smaller ones and parallel them. The Honda and Yamaha are the most quiet that I've heard but a little spendy so be prepaired for that.
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Old 01-29-2007, 12:38 AM   #5
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Hi, fact is, I never timed it, but I never run out of battery power again with lights on all day and part of the night. The only exception was when these batteries died due to old age, then got replaced as a pair again. Two is far better than one.
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Old 01-29-2007, 06:16 AM   #6
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Go 6 Volt!

If you are really looking for superior run times when in the boonies.....look at a couple of 6 VDC golf cart batteries. They are constructed to be charged and discharged every day, have way more amp hours available than a couple of GP24 or GP27s, and will last for many more charge/discharge cycles. If you look at the chart on the site below, you'll notice that the GPL-6C has more minutes of discharge available than even the HUGE 8D battery that weighs over 125lb each. They get my vote!!

If you want the BEST (and also most expensive), go with a pair of Lifeline AGM GPL-6C batteries. No maintenance, outgassing or corrosion! Lifeline Marine Batteries - AGM Marine Battery

One more thing, NEVER use dissimilar batteries in a 2 battery set-up. You should only use the same brand, size and preferrably, age of battery. If you plan to add a second one, buy 2 at the same time.
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Old 01-29-2007, 06:59 AM   #7
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Quote:
Originally Posted by lewster
If you want the BEST (and also most expensive), go with a pair of Lifeline AGM GPL-6C batteries.
Lew,

I can't find a GPL-6C battery anywhere on that site or elsewhere.

Did you mean the GPL-4C ?
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Old 01-29-2007, 08:59 AM   #8
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David -- Group 24 & 27 lead acid batteries shouldn't be discharged below 50%, so you don't want to be running til the lights dim. Doing so will significantly cut their capacity and durability. The same rule applies whether they are deep cycle or automotive. AGM batteries are better at this but I don't have the numbers in front of me.
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Old 01-30-2007, 06:25 AM   #9
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Ooooppppssss!

Quote:
Originally Posted by markdoane
Lew,

I can't find a GPL-6C battery anywhere on that site or elsewhere.

Did you mean the GPL-4C ?
Sorry, It IS the GPL-4C I was referring to. Must have had 6 volts on the brain!!!!!
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Old 01-30-2007, 06:30 AM   #10
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Quote:
Originally Posted by Canoe stream
David -- Group 24 & 27 lead acid batteries shouldn't be discharged below 50%, so you don't want to be running til the lights dim. Doing so will significantly cut their capacity and durability. The same rule applies whether they are deep cycle or automotive. AGM batteries are better at this but I don't have the numbers in front of me.
Even a deep discharge like this will create havoc on any lead acid battery, causing severe sulphation on the plates, which is very difficult to remedy. A 25% discharge is closer to the working bottom for a lead acid type.

AGMs, especially the 6VDC golf cart type, can be drawn down to 50% without any damage. I've heard of some being discharged to 8.5VDC (or effectively 75% discharge) so that NOTHING WORKED, but did no damage to the batteries.
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Old 01-30-2007, 10:23 AM   #11
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I just purchased 118AH AGM's weighing 99.4 pounds each.

If I discharged the battery in one hour it would produce 81AH.
If I discharged battery (2.06A drain per hour) over 72 hours its net output is 148AH.

So the rule is: Slow the discharge rate down and the chemical processes are inheriantly more efficient.
Two batteries will definately slow the discharge rate versus a single battery & almost magically add the equivelant of a third battery, no BS.
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Old 01-30-2007, 11:36 AM   #12
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I think RoadKingMoe answered this question very eloquently (and mathematically) a few months ago.

Here' the link:http://www.airforums.com/forum...15-post23.html
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