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Discussion Starter #1
My Mariner 39 currently has 6 6 volt golf cart batteries which are in configured into 3 banks of 2 batteries (in series) each.

It is about time to replace them. What is the advantage of this set up over:

1. three twelve volt batteries in 3 banks of one battery each or
2. 6 twelve volt batteries in 3 banks, two batteries per bank.

Thanks.
 

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Discussion Starter #2
The advantage of 6VDC batteries is first of all cost per unit. Second is the fact that 6VDC batteries with very high Amp Hour Ratings can be purchased in pairs for less than one 12VDC battery that comes close in Amp Hours.

The 6VDC Batteries will discharge and recharge more times than 12VDC batteries will, so their life span is greater.

If you buy 6VDC batteries or 12VDC batteries make sure that you get the highest Amp Hour Rating you can on a deep cycle battery... not cranking amps. The 6VDC bats will crank your engine without any problems. If cranking is a concern you can always set it up so you have a 12V battery to kick your engine over.

I''m putting in new batteries here pretty soon and I''m going to go with 4 banks of double 6''s.
 

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Discussion Starter #3
rob,
i don''t understand wht a 12 volt battery has a shorter life span the a 6 volt one. could you please explain?
thanks
eric
 

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Discussion Starter #4
i believe the new thinking is having one humongous house battery bank and a small engine start bank each totally separate maybe with a combiner for charging and a combiner switch for emergencies and a smart battery monitor.
eric
 

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Discussion Starter #5
As I understand it....the difference in the longevity of 6VDC and 12VDC batteries is because 6VDC batteries were always intended for long slow discharge periods..like golf carts and such. 12VDC batteries were developed more for cars, with short duration high outputs for starting and quick recharging. Even in boat usage its hard to find a pure 12VDC batterie that does not state its "cranking capacity" in its description. I think that most of the 12VDC "DeepCycle" batteries were intended for "bass boats" so they could crank and run a trolling motor. Surrette and Rolls are trying to correct this differentiation....but then you have to consider the cost of their batteries.

At this point, as much as I would like to have a large bank of their batteries, I would like to have a new Lamborghini too. But lets face it....$1200 to $1600 for FOUR batteries? I can buy alot of 6VDC''s for that kind of money!!

I have been looking at West Marine''s 6VDC Marine Deep Cycle batteries...rated at 225 Amp Hours...and am considering a bank of 8 of them, switched in pairs but operated as a large bank.... They have a good warranty on them and they sell for $89.99 each in their stores...at least down here. So for $700 I can get 900 amp hours and save a ton of money. And these batteries were made for the marine envioronment. But there are other batteries made for golf carts that are probably as good and cost less.

Don Casey is certainly a believer in the 6VDC golf cart batteries....

And yes, even Nigel Calder has expressed his feelings in writing that one large bank of batteries being used constantly is more efficient and economical than small independent banks being "rotated" for use.
 

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Discussion Starter #6
One other small item.... I just found out today that the 6VDC batteries that BOAT/US sells in their stores and through their catalogue are 226 Amp hour rated. Their price is about the same as West.
 

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WHY 6 VOLT BATTERIES ARE BETTER THAN 12.

For the same ampere hours, if you could get it all in one 12 volt battery, there would be no difference - a 12 volt battery has two 6 volt batteries in series inside it.

BUT for the same ampere hours, if it is going to take two batteries to do it because of size, weight, availability, etc., then rather than two 12 volt in parallel you are better off with two 6 volt in series.

Why is that you ask?

Because batteries in parallel, even if twins from the same manufacturer''s batch, will never be exactly identical, so one will always be a little weaker than the other and when charging ceases, the weaker one will discharge, or steal some of the charge from the stronger one through the parallel connection. This may be minor when they are new but as they age, the problem will get worse.

On the other hand, batteries in series can''t discharge into each other, so for that particular setup, the pair of 6 volt will be better.
 

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Discussion Starter #9
i found the trojan #27 batteroes at 115 amp each are a great buy at about $90-
have been using them CONTINIOUSLY for a year now and they charge and discharge still within their specs. we equalize them monthly.
eric
 

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Discussion Starter #10
But aren''t type 27''s usually "starting" batteries??

I presently have two NAPA "Premium Deep Cycle Starting" batteries....type 27''s that are about $130.00 each....and in general as a liveaboard whose refrigeration is on all the time....I''m not too impressed. Also have two 6VDC Golf Car batteries...they are older and probably close to replacement age.

I guess the biggest single difference though is the fact that the 6VDC''s have more recharging cycles in them than any of the 12VDC batteries.
 

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Discussion Starter #11
type 27 is a size not a type of battery it is a vailable in starting as well as deep cycle.
for my boat i use 4 deep cycle in parallel (and am planning to go to 6) for the main bank and two deep cycle for the starting bank. i oversized the starting bank and used dep cycles so if i have a problem with my main bank i can fall back on the other bank.
i found that the trojan brand has the largest # of amp hours for their size.
eric
 
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