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Old 04-26-2020, 07:55 PM   #15
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First let me start with the fact that I know nothing about electricity except ON and Off.

The house batteries in my unit are 2 6V in series and I was wondering why it is 6V in series rather than 2 12V in parallel?

Is there a good reason for this?
Because the 6V batteries are TRUE deep discharge (likely they are golf cart batteries) and will last longer.
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Old 04-26-2020, 08:08 PM   #16
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Math time! Watts equal volts times amps.

Watts never change, that's there the power is used. Volts and amps vary inversely to each other. Twice the voltage equals half the amperage to deliver the same load (watts). Combining two 6V batteries in series doubles the voltage, the amperage remains the same as the smallest in the array (try to avoid mismatching batteries). Combining two batteries in parallel doubles the AMPERAGE while the voltage is the same.

The reason that the RV industry uses 2 (or more) 6V batteries in series groups of two to make a 12V array, is that the golf cart batteries have MUCH thicker plates than the normal automotive starting battery (which usually have a lead "mesh" or "sponge" form that makes for a LOT more surface area, and higher amp delivery ability... At the tradeoff of much lower capacity. Even so called "deep cycle" 12V batteries are shorter in height than the GC2, which means each cell has less total amperage capacity even as it still is 2 volts per cell. And the plates aren't as thick as the golf cart battery so they can't sustain true deep discharges.

GC2 batteries tend to be around 85 lbs each, where a group 65 12V battery is somewhere around 60 lbs. That's a LOT of missing lead in that 12V battery.

It isn't a great idea to draw any lead acid battery below around 50% state-of-charge, but the GC2 can handle it better than the deep cycle marine or automotive starting batteries. Don't let them sit around depleted though, charge them right back up if you do inadvertently drain them. The longer they sit at low power, the more sulfates grow on the plates and reduce the total capacity of the battery.
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Old 04-26-2020, 09:22 PM   #17
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Thanks to all for the information posted!
This is a great site for knowledge and experience- I consider myself lucky to have been able to find and use this site for the collective knowledge that is here and so readily shared.
Thanks again for the posts!!!
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Old 04-26-2020, 09:49 PM   #18
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the simple answer is true deep cycle 12 volt batteries are quite expensive
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Old 04-27-2020, 05:25 AM   #19
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In starting applications a 6 volt motor will draw twice the amps as a 12 volt starter motor.
True and twice as much amperage mean twice as size of the wire ! Same with everything else on the car.
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Old 04-27-2020, 05:28 AM   #20
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the simple answer is true deep cycle 12 volt batteries are quite expensive
And difficult to find ! Probably only at a golf cart distributor or a solar store.

Trojan T-1275
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Old 04-27-2020, 06:25 AM   #21
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Thanks to all who have 'helped to educate me" If two 6's are the best way to go because of plate size capacity etc. why did the automotive industry abandon the 6V battery?

My old old ('53 Plymouth Mayflower) is 6V and the hand held spot light that is a genuine Mopar accessory is 6V.

I am not trying to promote an argument just wondering why 6V was abandoned if it is better in this (RV Application)
Starting is a very different situation than house needs.
House needs deep cycle ( low amp draw over extended time) start is the opposite (hi maps short duration)
To optimize batty performance the design has to be different. See...
https://marinehowto.com/wp-content/u...le-Battery.jpg
So called marine / RV dual purpose battys are just a compromise. Will do both but not optimized for either. For RV house needs true deep cycle are the best bet and 6V GC golf cart batty are the lowest $/AH as they are a high vol item.
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Old 04-29-2020, 08:23 AM   #22
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And difficult to find ! Probably only at a golf cart distributor or a solar store.
Not hard to find. Sam's Club, Costco, Bulbs Plus, O'Reilly, Napa and many auto other auto parts stores carry them.
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Old 04-30-2020, 07:21 AM   #23
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Not hard to find. Sam's Club, Costco, Bulbs Plus, O'Reilly, Napa and many auto other auto parts stores carry them.
I just bought 8 from local Sam's Club for $170 ea.
Hard to beat $/ AH and I've had good luck w Duracell / East Penn AGMs.
If you are looking for a higher $ specialty batty you likely won't find them locally but GCs or GP31 AGM or FLAs are VERY common and available.
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Old 04-30-2020, 01:31 PM   #24
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I just bought 8 from local Sam's Club for $170 ea.
Hard to beat $/ AH and I've had good luck w Duracell / East Penn AGMs.
A pair of 6V GC2 Duracell batteries will run you about $180, but will give you about 220 Ah vs a GC12 which will give you about 155 Ah.
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Old 04-30-2020, 09:18 PM   #25
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A pair of 6V GC2 Duracell batteries will run you about $180, but will give you about 220 Ah vs a GC12 which will give you about 155 Ah.
And if you keep them at a 50% SoC as your low point, that's 110 usable amps from the GC2 pair, or about 77 from the single 12V.

I also know from experience that the GC2's larger plates will tolerate a deeper discharge more readily (especially when charged up within an hour or three of hitting the low point - Mine would only sit that long at most b/c of my solar system) where the recovery performance of the 12V single is unknown b/c I've never used one like that.

The instances of pulling them below 50% SoC in my usage is entirely unintentional, and also somewhat unconfirmed b/c I was actually having some wire issues from a bad switch and corrosion that I recently discovered and fixed. So the low voltage might actually NOT have been that low but the switch resistance was messing with it.
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Old 05-01-2020, 06:33 AM   #26
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And if you keep them at a 50% SoC as your low point, that's 110 usable amps from the GC2 pair, or about 77 from the single 12V.
The only battery chemistry that I know of that can tolerate multiple discharges to near 0% SOC is lithium.
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Old 05-01-2020, 06:49 AM   #27
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A pair of 6V GC2 Duracell batteries will run you about $180, but will give you about 220 Ah vs a GC12 which will give you about 155 Ah.
Correct... mine were the AGM variety... and run about 2X$ of FLAs
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Old 05-01-2020, 08:13 AM   #28
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Oops -- meant to quote Gary RVRoamer.

Excellent answer. Quick note: 12V deep-cycle batteries are always available from marine suppliers, but not at a cost savings -- usually the opposite. (Boats, planes, race horses . . . )
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