6v bank vs 12v bank

[CaptMDG]

What are the pros and cons of having either 1) two six volt batteries in series producing 450 AH, or 2) two twelve volt batteries (225 AH each) in parallel producing 450 AH. I am interested in the practical physics of these configurations. On paper they are the same, or are they?


I am not interested in costs, sizes, or weights of each bank, just in the practicality of each.

[markcouz]

If they are flooded cells (which they sound like) then I would personally prefer the 2x 6v batteries with 6 cells to maintain (3 each), rather than 2x 12v batteries with 12 cells to maintain (6 each) - otherwise no difference if they are the same make, chemistry, quality etc.

[Pete7]

Likely the 6v batteries if flooded lead acid (FLA) will have a much higher number of cycles, therefore if everything else is equal a longer life. Worth choosing a manufacture and comparing the specs.

Perhaps one down side is if one 6v battery fails, you are stuffed. One 12v battery going down if caught in time could be removed and you limp on temporarily until it can be replaced.

The golf cart 6v batteries won't fit, so sadly we have 2 x 12v, but would choose the 6v in preference.

Pete

[mikeo16]

2 6-volt batteries in series = 225 amps at 12 volts.
2 12-volt batteries in parallel = 210 amps (assuming they are 105 amps each for group 31)

[Pete7]

Originally Posted by mikeo16

2 6-volt batteries in series = 225 amps at 12 volts.

Oops well spotted.

[Dsanduril]

The OP has specifically said that the final bank has the same capacity, he is interested in the pros/cons of parallel vs. serial configuration.

The point about number of cells is well taken - with two batteries in each system there will be half as many cells in a 6V pack.

However, my preference would be the parallel installation for two reasons:

• Balancing is easier and can be done with the on-board chargers if required.
• Still have a usable battery if one dies.

I know that this can get quickly complicated and others will say the opposite, that's my brief take from my experience.

[Cheechako]

I'd go with whatever weighed more. More weight = thicker cell plates. Likely the 6V version.

[S/V Illusion]

The whole “if one fails” argument seems pretty lame. How many people have only one bank of 2 -6V batteries? Or one 12V battery? In either case, “if one fails”, who’s bad landing is that?

[john61ct]

Originally Posted by CaptMDG

I am not interested in costs, sizes, or weights of each bank, just in the practicality of each.

Well all those are practical issues,

The key metric is $ per Ah per year of use, and also take into account the inconvenience of more frequent bank replacement.

But OK. . .

For true deep cycling usage, you need batteries specifically designed to last many hundreds of cycles still performing well.

99.999% of 12V batteries on the market do not meet that criteria, certainly none sold in big box retail or automotive channels, only suitable for cranking engines no matter what the label or their marketing copy fraudulently claims.

There is only a handful of manufacturers of good quality in the market.

95% of their units sold for that purpose come in lower voltage units that need wiring in series to get to 12V.

Most end up costing a lot more per Ah than a Wally world special.

Except for 6V golf car batteries, cheap as chips **and** perform very well, can last 8+ years even cycled daily.

Of course each market is different, but the above is triply true for North America.

That said, this is not a technology issue, but a market reality.

There are a few vendors producing most excellent 12V batteries for deep cycling, including in 4D & 8D automotive sizes.

But they are harder to find, and more costly per Ah.

https://marinehowto.com/what-is-a-deep-cycle-battery/

[Navicula]

have this setup of four six volt batteries in series and then parrellel to make one big bank...they are 105 amps , but i have no idea what the total amp hours would be...
however they work well like this and easier to handle....I dont think I would ever go back to 12v batteries

[john61ct]

Here is a technical consderation.

The fewer the number of series strings in parallel, the better, excluding redundancy concerns.

Getting higher Ah per cell helps keep the number of strings down.

The ideal is 2V cells, anything higher (4/6/12V cells) are packaged strings of 2V cells already.

If you only need say 3-500Ah, then 3 strings of 12V cells is getting to the point where imbalance issues will reduce lifespan.

Past that much worse.

If redundancy is required, then two strings is the ideal.

Lower voltage cells also don't break your back as much.

[john61ct]

Originally Posted by Navicula

have this setup of four six volt batteries in series and then parrellel to make one big bank...they are 105 amps , but i have no idea what the total amp hours would be

6V 105Ah

2x in series makes 12V 105Ah
then those strings in parallel means 12V 210Ah.

Same as one pair of 210Ah 6V, but then no redundacy.

[john61ct]

For the NA market

The best deep cycle battery value by far is Duracell (actually Deka/East Penn) FLA deep cycle golf cart batteries, 2x6V, around $200 per 200+AH @12V pair from BatteriesPlus or Sam's Club.

Deka labeled same batts are also sold at Lowes.

[mikeo16]

The Deka 6-volt st lowes.com are 230 amps
https://www.lowes.com/pd/Deka-6-Volt...ttery/50183775. At $144 each are a great deal for batteries that will get far more cycles than your typical 22 volt deep cycle battery

[mikeo16]

Oops fixing typos it should have stated "than your typical 12 volt battery "