12v to 6v review?

Gdetrailer wrote:

mr_andyj wrote:
batts dont typically just die. They start to die slowly. With two 6's one might be going bad, the other still is good. The two add together to still give you enough volts to do everything. 11.5 is low, but 5.75 plus 6 is 11.75 which is still pretty good. With one 12 volt batt only able to get to 11.5 and the other 12 then the total voltage available is still 11.5. The bad batt brings down the good one. when parallel, but not when in series. This is the big reason to go with two 6's. You can mis-match two 6's in series, but you really should only exactly match when in parallel (two 12s).
Nonsense? No. Good advice, but go do an easy forum search as there are many post on this same topic and easy easy to find with a few keystrokes....

You do realize that "lead acid" batteries are nominal 2V per cell, right?

To get a "12V" lead acid battery, it takes six 2V cells which are wired internally in series to arrive at nominal 12V. A "12V" battery just combines all 6 cells into one box.

To get a "6V" lead acid battery, it takes three 2V cells wired in series to arrive at nominal 6V. A "6V" battery combines 3 cells all in one box.

There is nothing "magical" about a "12V" battery compared to a "6V" battery other than the fact that it takes two "6V" batteries wired externally in series to achieve nominal 12V.

The sticking point many point to is using 6V batteries ends up with a higher "internal resistance" than if you used two "12V" batteries in parallel.

All battery cells have something call "internal resistance". Internal resistance causes a high voltage drop under high current draw.

So, to get around the internal resistance issue folks insist that 12V batteries are better because the internal resistance is reduced when in parallel, which is sort of true to some extent.

However, they do so at a loss of capacity when you compare the physical size, weight and Ahr capacity.

Not to mention 12V batteries actually have a higher internal resistance due to less plates, smaller plates and less surface area on those plates. But in electronics when you parallel resistors the overall resistance is reduced (Ohms law) so the end result may be a bit less voltage drop when paralleling two 12V batteries when using very high current draw devices.

A group 27 12V battery is roughly the same size as a 6V GC2 but the GC2 is a bit taller and weighs more than a group 27.

one group 27 has roughly 80Ahr of capacity and max usable capacity of 40Ahr (50%) for rated life.

6V GC2 has roughly 210 Ahr capacity and max usable capacity of 168Ahr (80%) for rated life.

Granted, you need two 6V GC2s (series wiring of 6V batteries does not increase Ahr capacity) but from my POV 168 Ahr is considerably much more usable capacity than three group 27 12V batteries wired in parallel.

Personally, if internal resistance bothers you, go with four 6V GCs and wire up as two series strings of batteries and parallel the two series strings. End result will be far more usable Ahr capacity with low enough internal resistance than using four 12V batteries in parallel.

actually most 12V batteries have lower internal resistance than a comparable AH 6V because they have more and thinner plates per 2V cell than 6V. But the thinner cells and associated tradeoffs means lower cycle life and not likeing deep discharges.

But yes, using four 6 volt will give about 500AH capacity and suitability for reasonably high current draw. But four 12V in parallel will still give lower voltage drop due to lower internal resistance and load sharing amongst four batteries instead of two.