12V vs 6V batteries for house bank

bansil

Adventurer
Which is a "better" setup? and why?

2 12V deep cycle batteries with 215 Ah each equals 430 Ah of 12V

4 6V golf cart type batteries with 215 Ah each equals 430 Ah of 12V

So price wise they are both close (wifes cost) so batteries weigh about the same (real close)

So we have 2 banks one is twice the size and twice the wt as the other

Which way to go?

I assume the 6V batteries can be "abused" more than the 12V

I went with 2 and 4 just for numbers it could be 4 and 8 same thing

TIA
 

Jonathan Hanson

Supporting Sponsor
Simple answer: Even if your total amp-hours are the same, six-volt batteries will normally be more robust, since they have only three cells per battery rather than six, and thus can use thicker lead plates. Usually the six-volt option is slightly less expensive per amp-hour as well.

Our home solar system (completely off-grid) comprises six-volt batteries wired in series to create a 12-volt system.
 

cwsqbm

Explorer
2 12V deep cycle batteries with 215 Ah each equals 430 Ah of 12V; 4 6V golf cart type batteries with 215 Ah each equals 430 Ah of 12V

So price wise they are both close (wifes cost) so batteries weigh about the same (real close)

Typically, a 200Ah 12V would be the same weight as a 400Ah 6V battery, since both batteries would be storing 2.4KWh.

So the comparison should be between two 200Ah 12V batteries in parallel vs two 400Ah 6V batteries in series. Both setups have the same energy - 4.8KWh, roughly the same weight, and probably similar cost. However:
(1) With the 2 12V setup, each battery has 6 cells, for a total of 12 cells between the two. The 6V batteries have 3 cells each for a total of 6 cells. Therefore, each cell is bigger in the 6V batteries.
(2) even with two "identical" 12V batteries, there will be a little imbalance between the two. The same current doesn't flow equally through both 12V batteries. Not majorly significant, but it doesn't happen at all with the 6V batteries because they are in series, not parallel.

One disadvantage (in theory) of a 2 6V batteries is that if one cell dies, you're entire system is dead. Lose one cell in the 12V setup, and you've only lost half your capacity, assuming the batteries are isolated in some way from each other so as the dead battery doesn't kill the other one.
 
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pods8

Explorer
So we have 2 banks one is twice the size and twice the wt as the other

If your ah is the same then the banks physical size will generally be the same. A 210ah 12V battery is a BIG battery (like probably 120-140lb big). Something like the die hard 31M is only a 100ah battery, you sure you looked at the right numbers based on thinking one setup would be smaller than the other?
 

bansil

Adventurer
Honestly i don't have a clue, I told my wife I wanted 4 6V 205/215 Ah batteries (straight from factory only a week old)

She came home with numbers the battery rep had given her and he convinced her to ask me if 2 12V 210Ah would work? supposedly same "size" each and about $150 each...so it would be smarter to have less wt and less room taken up and be cheaper...my mind could not figure out how 1/2 storage size and wt could be equal

I will try to get some spec's tonite,

I thought the 12V would have to be about the size of my 8D starting battery so I figured 6V size would be easier to move :sombrero:

Thank you
 

pods8

Explorer
Honestly i don't have a clue, I told my wife I wanted 4 6V 205/215 Ah batteries (straight from factory only a week old)

She came home with numbers the battery rep had given her and he convinced her to ask me if 2 12V 210Ah would work? supposedly same "size" each and about $150 each...so it would be smarter to have less wt and less room taken up and be cheaper...my mind could not figure out how 1/2 storage size and wt could be equal

I will try to get some spec's tonite,

I thought the 12V would have to be about the size of my 8D starting battery so I figured 6V size would be easier to move :sombrero:

Thank you

A 210ah 12V battery would typically be an 8D unless you're talking something specialty.
 

cwsqbm

Explorer
If you want a comparison with numbers, look at this chart from Lifeline batteries (others manufacturers will be similar). You'll see that for a given energy capacity, all wet-cell deep cycle lead acid batteries set ups will weigh roughly the same. You won't save any weight or size between 2 6V and 2 12V batteries.
 

bansil

Adventurer
The 12V battery was the same size and is an "RV" battery rated like you said at 1/2 the Ah of the 6V, the "battery guy" didn't have a clue about Ah and it's use

He just assumed that 2 of the "RV" batteries would be better than 4 of the 6V ones :yikes:

I looked at the chart and showed him that it was 1/2 the Ah and the one that matched the Ah of the 6V was an 8D

So thank you all for my reassurence and I told him I will go with 4 of the 6V to start with I am not screwing with 8D's too heavy and not cheap to replace "on the road"

Thanks
 

Alastair D(Aus)

aging but active
cross discharge

If you can manage with 2 x 6v batteries in series then they are preferable to 2 x 12v batteries in parallel. No 2 batteries are exactly the same and when everthing is turned off the 12v batteries will compete and 1 will slightly discharge the other. If they are the same type and age then the effect is probably not a problem otherwise you need to isolate then when not in use. If you have a constant standby charger then it doesn't matter.

I am currently looking at using 6 x 2v (single cell) batteries of the type that are used in solar power systems. I am having trouble finding out if they are suitable for a mobile situation and will handle the road shocks.

cheers
 

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