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6 volt Batteries vs 12 Volt Batteries


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All things being equal (which they are not)

 

I have 2 6v deep cycle batteries in series getting 12 v and I am wondering why didn't they put 2 12 volt batteries in parallel.

 

Both end up giving you 12 volts. I know the amperage changes.

 

For example

 

2 6 V batteries in series

6 Volt 500 amp if there was such a thing) would give you 12 volts with 500 Amps

 

2 12 V batteries in parallel at 250 amps would give you

12 volts with 500 amps.

 

I understand there would a cost difference.

 

So why go with one over the other if cost is not a factor? Also I think if I am on 6 volts batteries and go to 12 volt batteries o would have to change out the charger too.

 

Your thoughts.

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As far as your charging goes 12V is 12V nothing changes but two 6 volt batteries will give you lot higher amperage then 1 12V.

 

Now put in 4.....6V batteries and your amperage will be way above what two 12V batteries can give you. I see your thinking but you have to replace each single 12V with 2 six V to get the higher amperage. Plan on packing some weight around if you do this.

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In series, Voltage is additive (6 + 6 = 12) HOWEVER Amp Hours (Or say Cold Cranking Amps) is NOT additive. For example if you had two sixes in series each rated for say 200 Amp Hours, you still only have 200 Amp Hours of stored energy (at 12 volts). If you had two batteries rated at say 500 Cold Cranking Amps in series, YOU STILL ONLY HAVE 500 CCA.

 

In parallel voltage is NOT additive HOWEVER Amp Hours (Or say Cold Cranking Amps) IS additive. If you had two 200 Amp Hour 12 volt batteries in parallel, you end up with 400 Amp Hours of energy storage at 12 volts. Similar, two batteries rated at say 500 CCA in parallel gives you 1000 CCA

 

One consideration is that true deep cycle 6 Volt golf cart batteries (I'm NOT talking Semi Deep Cycle Hybrid so called RV/Marine Batteries) are more readily available and common and in stock on the shelf and easier to purchase then true deep cycle 12 volt batteries. Trojan and others make true deep cycle 12 volt batteries but you don't see them on dealer shelves like the much more common 6 volt units. On Wally World shelves you may see 12 volt semi deep cycle hybrid RV/Marine Batteries or 6 volt true deep cycle golf cart batteries, but you don't see many 12 volt true deep cycle units.

 

These numbers are ONLY for comparison and contrast, you can buy different rated batteries then my examples above

 

John T

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As noted above, most 12 volt "deep cycle marine/rv" batteries are not truly DEEP cycle batteries, they are a hybrid between a deep cycle and a starting battery. If the battery has a CCA (cold cranking amps) rating it IS NOT really a deep cycle battery. Instead look for AMP/HOUR ratings.

 

The deep cycle marine/rv batteries will work well in most peoples application - limited boondocking. However, if you plan to boondock much, you should consider true deep cycle batteries. I believe virtually all 6 volt batteries are true deep cycle batteries.

 

Regarding 12 volt or 6 volt.... Assuming both have the same amp/hour ratings .... both will give you exactly the same storage capacity. Where the difference between 12 and 6 comes into play is the internal resistance and the connection resistance of each battery. These will never be exactly the same for both batteries resulting in one battery getting a higher charge (or discharge) than the other so you end up with one 'working harder" than the other.

 

With two 6 volt batteries ALL the charge (or discharge) current passes through BOTH batteries and is equal resulting in both "working" equally.

 

Now when you increase to 4 or 6 batteries you get back into the same issue as with two (or more) 12 volt batteries.

 

Hope this helps you to understand better,

Lenp

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In addition, if you have only two batteries, placing them in series provides a more effective charging capability and assuming that the physical size of the two batteries (12V or 6V) is about the same, you will have roughly the same amount of power capacity in watts with either configuration. But series cells will all charge to full capacity even if one is not as good condition as the others, while parallel cells will only charge to the level of the weakest cell. There is a lot of battery theory involved in this sort of debate and not all of us who are educated in electrical theory agree. But based upon my own experience, I consider the paired 6V a better choice, but the difference is not a major one. As others have mentioned, it is partly a matter of the availability of the highest quality of deep cycle batteries. Because they are used in most golf carts, they are very easy to find while the pure deep cycle 12V battery can be more difficult.

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Another thing to look at is the lifetime cycle (charge/discharge) rating. For a lot of the batteries I've looked at the pair of 6 volt batteries has a longer rated lifetime than similar sized 12 volt batteries.

 

Wiring properly so you have equal current paths will help keep paired 12 volt batteries more evenly charged, something that is also important if you have more than 2 six volt cells. Specific gravity monitoring and equalization when needed will prevent problems with unequal charging/discharging.

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I don't know where this observation of mine fits into any decision about 6ers or 12ers... but here goes.


Both 6v and 12v batteries are 2- volt cells in series. A 6v battery is not 3 6v cells in parallel. Are battery makers constrained to 2v cells by physical design/chemical properties, or, are series connections preferred over parallel ones?

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The 2 volt cells are a result of the lead-acid chemistry, different cell materials would give different voltages but for the most part lead-acid (flooded or AGM) are the sweet spot for most uses today.

 

Series connections are best in my opinion, with only one string of cells you avoid the issues with multiple current paths. Sadly once again cost enters into the picture and getting big enough 2 volt cells to make your battery bank just isn't really the inexpensive route so most folks compromise on multiple strings of pairs of 6 volt three cell batteries.

 

http://bigtimebattery.com/store/trojan_replacement_ind27-2v_battery.html?gclid=Cj0KEQiA3t-2BRCKivi-suDY24gBEiQAX1wiXMoTvoQpKPWI29MJlZxmOmthTd5St2-fEj5mYHFUvGMaAnv78P8HAQ

 

IND27-2v_large.jpg

 

or

 

http://webosolar.com/store/en/deep-cycle-batteries/923-surrette-s-1660-ah-2-volt-deep-cycle-battery.html

 

surrette-s-1660-ah-2-volt-deep-cycle-bat

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The first thing to remember is that these cells are not actually 2V but range from about 1.5 to 2.3V each, depending upon the state of charge. It is the chemistry that determines the voltage of each cell an a lead acid battery can increase the voltage by increasing the acid to water mix of the electrolyte, but that also will shorten the life of the cell. A typical flashlight battery is also a single cell that is connected in series to increase the output voltage by putting them in end to end. That type of cell is a nominal 1.5V. There are other voltage levels of cells but they are not in common use, for many reasons. The reason that gel cell batteries have a different recharging requirements is that the voltage swing from them is different. That is also true for the new lithium batteries now becoming available. The reason that you see batteries of 12V and 6V configuration is because the auto industry as adopted that voltage as their standard. Some golf carts are using multiples of 8V batteries.

 

Battery cells can be made far larger in order to increase the storage capacity of each cell. When I was in the sub service our emergency electricity supply came from a very large, lead acid, flooded cell battery that was made up of individual cells, each of which weighed in at 2000#. Each submarine battery consisted of 125 cells, all connected in series.

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I'm in Kirk's camp on the voltages. One typical number you often see is 2.1 volts per cell, which as he notes can depend on state of charge, temperature and other factors. Therefore, what are called "12 Volt" 6 series cell lead acid batteries typically measure around 12.6 volts at rest full charged. Here's a voltage chart found online.

 

Temperature: 77 degrees Fahrenheit

Percent Hydrometer Unloaded
charge reading voltage
100 1.265 12.63
75 1.210 12.30
50 1.160 12.00
25 1.120 11.76
0 1.100 11.64

 

Don't let your voltage drop now gang...............I don't like my house battery bank voltage to drop down much more then 12.3 (25% discharged) and 12 (50% discharged) is the absolute lowest level I would tolerate before firing up the genset and charger or pulling out into more sunlight.

 

I also prefer series connections when possible as each cell receives the same current and that's (current, the flow of electrons) what does the charging, but with four or more 6 volt batteries, you have to resort to some sort of series/parallel configurations in which case I adhere to Smartgauge recommendations.

 

 

John T

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