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Old 14-08-2015, 07:04   #16
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Re: Pros & Cons of 12 volt vs 6 volt batteries

I was not discussing whether 6-volt batteries in general lasted longer, or produced more cycles than 12-volt batteries. My point was that the more "components" in a system, the less reliable it became. In my example, using batteries with about the same physical sizes (group 31 (12v) vs GC2 6v), you will end up with about 450AH capacity. In the first case you'll have 24 cells which can fail, in the second only 12. So, by pure statistics, assuming that everything else about the batteries is identical, the bank of 12-volt batteries will be half as reliable. But as a number of posters have pointed out, everything else is never equal.

But not only does the parallel 12-volt configuration have more cells to fail, it has more connections to fail: 6 inter-battery wires for 12v configuration and only 4 for the 6-v configuration.
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Old 14-08-2015, 07:28   #17
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Re: Pros & Cons of 12 volt vs 6 volt batteries

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Originally Posted by kjdavie01 View Post
Hi Folks! Looks like we'll be needing to replace the house battery bank in our Triangle 32 before next season, so I've been asking questions. One of the "experts" I've consulted - with a lot of experience with house off-grid solar PV systems - stated that a pair of 6 volt batteries, wired in series, will charge more evenly and therefore have a longer lifespan than (as I'd planned) a pair of 12 volt batteries (group 27) wired in parallel. He could give me no technical description of why this would be so, but stated that two 12 volt batteries (hooked together) in a 12 volt system don't charge evenly, while two 6-volts wired together look like one battery and stay more evenly charged.

So, I'm dubious, but would love input from anyone with ADVANCED knowledge of battery systems. Please, if you don't know more than me, sit this one out. My internet time here on the boat is very limited. Thanks all!
Electrically there is no significant internal difference between 1 x 12V versus 2 x 6V batteries assuming their Ahr ratings are equivalent.

Equalization of 6V batts probably results in greater life. I've never conducted AB testing but some of the solar specialists would probably advocate for 6V in series over single 12V.

The benefits of using 6V batts, wired for 12 or 24V are:

1) Easier handling per battery
2) I cant think of any commonly available 6V batts that arent ruggedized. It can be quite confusing identifying a deep cycle versus some of the so called deep cycle 12V batts.
3) There tends to be more space in a 6V batt form factor to use thicker plate structures. Most of the more compact 12V batts trade off ruggedness for smaller size. Characteristics like shedding and high discharge rate plate distortion are minimized.
4) A single 6V battery failure has only half the impact of a 12V batt failure. Depending on configuration.

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Old 14-08-2015, 07:44   #18
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Pros & Cons of 12 volt vs 6 volt batteries

I believe the OP's advisor is right. Charging and discharging of a series bank is indeed more even, because every electron in the circuit flows through both batteries, while in a parallel arrangement, the electons 'split', with some flowing through one battery, and some through the other. Due to unavoidable differences between the batteries, wiring, and connections, this split isn't perfectly even. In a properly installed parallel bank with just two batteries, the effect probably isn't significant, but it is there. (This is a real concern in large PV arrays ashore, with multiple parallel strings).

And in contradiction to a previous poster, two batteries in series actually requires fewer connections and extra wiring (one jumper, four connections) than do parallel (two jumpers, six connections).

All in all, series seems to be a big winner over parallel.
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Old 14-08-2015, 08:38   #19
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Re: Pros & Cons of 12 volt vs 6 volt batteries

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Hmmm,

My house bank is two 4D AGM batteries. Replacing them by myself was not one of my better decisions, I have the crushed disk to prove THAT. In fact my back is still aching after 7 yrs.

My last boat had 6v golf cart batteries. How do my 4D's fare in this thread. Keep in mind I have limited access for maintaining wet cells.

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If you can fit them in, your better off with the GC's, especially if money is a consideration.
Now myself, I'm screwed, my battery box is 10" deep, meaning I can't fit GC's in there as they are too tall.
Near as I can figure, I can only use group 27 or 29, maybe 31 in 12V or go to these Lifeline Batteries - Marine & RV Deep Cycle Batteries.
But price these things, you have to sell your first born, so if I go that route, I'd better plan on being able to top them off to 100% very frequently to make them last.
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Old 14-08-2015, 09:32   #20
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Re: Pros & Cons of 12 volt vs 6 volt batteries

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Originally Posted by Rusty123 View Post
I believe the OP's advisor is right. Charging and discharging of a series bank is indeed more even, because every electron in the circuit flows through both batteries, while in a parallel arrangement, the electons 'split', with some flowing through one battery, and some through the other. Due to unavoidable differences between the batteries, wiring, and connections, this split isn't perfectly even. In a properly installed parallel bank with just two batteries, the effect probably isn't significant, but it is there. (This is a real concern in large PV arrays ashore, with multiple parallel strings).

And in contradiction to a previous poster, two batteries in series actually requires fewer connections and extra wiring (one jumper, four connections) than do parallel (two jumpers, six connections).

All in all, series seems to be a big winner over parallel.
Sorry - gotta disagree.

So one 12v battery - one positive cable and one negative cable to supply boat systems and receive charging

Replace the one 12v with two 6v batteries (in series - which is how the 12v cells are connected internally without an external cable) and you need one extra cable to connect the negative terminal on one 6v to the positive terminal on the other 6v battery. You still need the original positive and negative supply cables.

If you have two 12v batteries in parallel originally (most common configuration on boats) you need an additional two series cables to convert them to four 6v batteries. And so on. You will always need more cables for two 6v batteries to make 12v systems.

And the correct wiring of 6v batteries wired in series and then paralleled for more amp-hours prevents any problems with charging. And even if there is a miniscule, slight difference (which I have never heard of but might exist), you still have to parallel batteries at some point to add capacity. That is unless you can fit two gigantic 6v batteries in series to provide the same capacity. There's no free lunch with this stuff.

I grant you that there may be some small differences but those are unavoidable in real life. You put everything together as best you can using the best materials and workmanship and go on. If you are dealing with MW PV arrays for huge projects then you can invest in some engineering and much more costly equipment and materials. I promise you though - you will never measure a significant difference on a typical boat system. And then as soon as you did that, something else would happen in the batteries themselves that would skew the works, either plus or minus.
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Old 14-08-2015, 09:45   #21
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Re: Pros & Cons of 12 volt vs 6 volt batteries

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If you can fit them in, your better off with the GC's, especially if money is a consideration.

Now myself, I'm screwed, my battery box is 10" deep, meaning I can't fit GC's in there as they are too tall.

Near as I can figure, I can only use group 27 or 29, maybe 31 in 12V or go to these Lifeline Batteries - Marine & RV Deep Cycle Batteries.

But price these things, you have to sell your first born, so if I go that route, I'd better plan on being able to top them off to 100% very frequently to make them last.

A64pilot, are your battery boxes molded into your boat interior or can they be replaced? When I went to 6v GC batteries 3 or 4 years ago I had to buy new battery boxes but I did have room for them under the quarter berth.


S/V B'Shert
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Old 14-08-2015, 09:46   #22
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Re: Pros & Cons of 12 volt vs 6 volt batteries

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6v golf cart batteries generally have much thicker plates than their 12v "deep cycle" counterparts. i.e. the 6v battery is truly a deep cycle battery where most of the 12v batteries are dual-purpose.

They're also relatively cheap. They're also much easier to handle than 4d or 8d batteries. Bang-for-buck, for a SLA, I'd _always_ go for 6v batteries.

Search this forum, any RV forum, you'll find plenty of responses on this specific question.
Yep, best answer. A series string is always better than parallel. If you want even greater capacity than the 220 ahr at 12 volts that a pair of golf cart batteries provide, and you don't want any single battery to be over 80 lbs for ease of replacement, go to (6) 2 volt cells in series.
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Old 14-08-2015, 11:49   #23
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Re: Pros & Cons of 12 volt vs 6 volt batteries

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Sorry - gotta disagree.

To one 12v battery - one positive cable and one negative cable to supply boat systems and receive charging

Replace the one 12v with two 6v batteries (in series - which is how the 12v cells are connected internally without an external cable) and you need one extra cable to connect the negative terminal on one 6v to the positive terminal on the other 6v battery. You still need the original positive and negative supply cables.

If you have two 12v batteries in parallel originally (most common configuration on boats) you need an additional two series cables to convert them to four 6v batteries. And so on. You will always need more cables for two 6v batteries to make 12v systems.

And the correct wiring of 6v batteries wired in series and then paralleled for more amp-hours prevents any problems with charging. And even if there is a miniscule, slight difference (which I have never heard of but might exist), you still have to parallel batteries at some point to add capacity. That is unless you can fit two gigantic 6v batteries in series to provide the same capacity. There's no free lunch with this stuff.

I grant you that there may be some small differences but those are unavoidable in real life. You put everything together as best you can using the best materials and workmanship and go on. If you are dealing with MW PV arrays for huge projects then you can invest in some engineering and much more costly equipment and materials. I promise you though - you will never measure a significant difference on a typical boat system. And then as soon as you did that, something else would happen in the batteries themselves that would skew the works, either plus or minus.
To some extent, we're talking about two different things. I (and the OP) am comparing two 6V batteries in series with two 12V batteries in parallel. You are comparing two 6V batteries in series with a single 12V battery.

It is certainly true that the wiring for a single battery is less complex than for a series pair. But for that comparison to be valid, the 12V battery would need to have the same capacity of 2 6V batteries (around 220 AH), which would be a large, heavy, expensive battery. The OP is considering more commonly available 12V batteries, which don't have that sort of capacity.

There is a way to create extra capacity without going to parallel strings -- the use of 2V cells as deckofficer mentions.

I agree however, that for typical boat applications, this is really angels on the head of a pin stuff.
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Old 14-08-2015, 11:56   #24
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Re: Pros & Cons of 12 volt vs 6 volt batteries

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A64pilot, are your battery boxes molded into your boat interior or can they be replaced? When I went to 6v GC batteries 3 or 4 years ago I had to buy new battery boxes but I did have room for them under the quarter berth.


S/V B'Shert
They are molded in and double walled, making it even more difficult to build a new box. Cost of a new box easily exceeds cost differential of the lifeline batteries, hence my statement of "I'm screwed"
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Old 14-08-2015, 11:57   #25
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Pros & Cons of 12 volt vs 6 volt batteries

Yes but you have a beautiful Island Packet molded around your batteries. Not too bad really.


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Old 14-08-2015, 12:22   #26
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Re: Pros & Cons of 12 volt vs 6 volt batteries

seems this thread has become about trying to split fine blonde hairs to win a silly point
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Old 14-08-2015, 14:06   #27
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Re: Pros & Cons of 12 volt vs 6 volt batteries

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seems this thread has become about trying to split fine blonde hairs to win a silly point
Perhaps. Or maybe it's about providing the OP an accurate answer to his question.
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Old 14-08-2015, 14:16   #28
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Re: Pros & Cons of 12 volt vs 6 volt batteries

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Perhaps. Or maybe it's about providing the OP an accurate answer to his question.
guess you didn't read all the thread, that was done by post 3
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Old 14-08-2015, 15:02   #29
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Re: Pros & Cons of 12 volt vs 6 volt batteries

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Originally Posted by jeepbluetj View Post
6v golf cart batteries generally have much thicker plates than their 12v "deep cycle" counterparts. i.e. the 6v battery is truly a deep cycle battery where most of the 12v batteries are dual-purpose.

They're also relatively cheap...
Agreed, we're now on Trojan 6 volt batteries, bought in the Caribbean and as a supplementary question, would love to know how/why they're so reasonably priced on the west side of the Atlantic:
Back in England I would expected to pay around US$600-700 for four 110 amp/hr 12v leisure/dual purpose batteries, this side of the Atlantic, the cost of same appeared to be nearer $800-900. 4 x 225 amp/hr Trojans meanwhile cost us less than $700 in the Caribbean, whereas back in Europe they'd be over $1200. What's the reasoning?
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Old 15-08-2015, 09:32   #30
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Re: Pros & Cons of 12 volt vs 6 volt batteries

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To some extent, we're talking about two different things. I (and the OP) am comparing two 6V batteries in series with two 12V batteries in parallel. You are comparing two 6V batteries in series with a single 12V battery.

It is certainly true that the wiring for a single battery is less complex than for a series pair. But for that comparison to be valid, the 12V battery would need to have the same capacity of 2 6V batteries (around 220 AH), which would be a large, heavy, expensive battery. The OP is considering more commonly available 12V batteries, which don't have that sort of capacity.

There is a way to create extra capacity without going to parallel strings -- the use of 2V cells as deckofficer mentions.

I agree however, that for typical boat applications, this is really angels on the head of a pin stuff.
My misunderstanding I guess. But 2v cells are just a different way to "package" the same capacity, but with even more "batteries", but perhaps with ready-made external intercell connections. There's still no free lunch here.
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