6V house batteries in series VS new 12v single

[Stumble]

The Amp*hour rating for deep cycles is directly express able by weight. A good deep cycle battery will store 1.9ah/pound give or take a bit for the casing. So if you want a 200ah battery you can use 1-100lb 12v or 2-50lb 6v batteries the choice is yours. Actually you could use 2v cells which are even lighter per cell, but it's a lot of connections.

The old standby was to lug around 150lb 8d 12v at 300ah. I would much rather move 2 6v at 75lbs each. And so will your boat. Almost every time I have installed 8d's something gets dinged, dented, or dropped no matter how careful you are. They adjust too large to manhandle.

[inspectr]

Thanks for the responses.

I'm leaning towards replacing same with same

[Uncle Bob]

Originally Posted by inspectr

Thanks for the responses.

I'm leaning towards replacing same with same

Hi, if you go that way I can definitely recommend batteries online, here in Sydney. The pricing was way better than most other places that I could find.
Cheers.

[ramblinrod]

Originally Posted by inspectr

I have had my Dufour 35 Classic for nearly 10 years.

The boat has a single dedicated 12V starting battery, replaced around 3 years ago and going strong

The house batteries are a pair of 6 Volters, in series, been there from before I bought the boat in 2008. Working perfectly until now

Last month, locking up the boat for a driving holiday in tasmania I forgot to turn off the battery breakers, and when I went back to the boat the house set was flat, engine battery started the engine and seemed to charge OK.
Kill the engine, ten minutes later the battery meter shows 11.0V and alarms.

Fair enough, 10 year old batteries are probably dead, and 10 years has got to be acceptable.

Two days later, needing to replace some corroded wiring on some the pumps (another story, why do boat builders use domestic un-tinned copper wiring in bilge and freshwater pumps, and then run them in inaccessible places with the wiring brace tied together with cable ties) went back to the boat, ran the engine for 2.5 hours and the batteries are 90% charged and running at 12.5V. I am going to replace the batteries anyway.

My question, what is the advantage / disadvantage of 2 x 6 Volters, VS one decent sized 12V current technology battery as a replacement - obviously, there is plenty of room in the battery recess, and the only complication may be the need to replace the cables??

2 x 6 Vdc GC2s typically = 220 A-hrs @ 12 Vdc
2 x 12 Vdc Grp 27s typically = 200 A-hrs @ 12 Vdc

Some claim GC2s live longer. I would agree that a premium brand like Trojan T105s, may last longer than a low me Grp 27, but
comparing apples to apples I just don't see a difference.

I try to dissuade customers from a 2x6Vdc house bank, because if one goes down the entire house bank is lost, whereas with 2 x grp 27s only half the capacity is lost.

[ramblinrod]

Originally Posted by ramblinrod

2 x 6 Vdc GC2s typically = 220 A-hrs @ 12 Vdc
2 x 12 Vdc Grp 27s typically = 200 A-hrs @ 12 Vdc

Some claim GC2s live longer. I would agree that a premium brand like Trojan T105s, may last longer than a low me Grp 27, but
comparing apples to apples I just don't see a difference.

I try to dissuade customers from a 2x6Vdc house bank, because if one goes down the entire house bank is lost, whereas with 2 x grp 27s only half the capacity is lost.

In your case, because someone has already modified the boat to use 2 x 6Vdc batteries, if it was done properly with the proper sized battery boxes and wiring, you're prolly best to replace with same.

[inspectr]

As I wrote in the original post, this set of house batteries has given ME nearly 10 years of service in what is a fairly lightly used boat. I guess that I can assume that the rest of the gear connected to the batteries is OK.
There is plenty of space for either option, but replacing same with same seems the smarter option.
As I understand it, the Dufour 35 Classic came with a 2 x 6V house bank and a separate heavy duty 12v starter battery. I dont think the previous owner modified the batteries.
Once again, thanks to those who posted and offered advice
RPW

[captainwireman]

What is it with batteries? I have two that are only topped off once a year in Fairbanks Alaska sitting on my porch that load test strong. 4 years now but they were only lightly used. Yet I keep reading about batteries that often fail prematurely. Is quality control lacking in some brands?

[StuM]

Originally Posted by captainwireman

What is it with batteries? I have two that are only topped off once a year in Fairbanks Alaska sitting on my porch that load test strong. 4 years now but they were only lightly used. Yet I keep reading about batteries that often fail prematurely. Is quality control lacking in some brands?

When a battery fails prematurely, it is almost invariable because of the way they have been mis-used. i.e incorrect battery size/construction type for the loads and/or inappropriate charging systems.

Edit: And in Fairbanks, they will not be exposed to the high ambient temperature that many batteries operate in - which can also be battery killer.

[conachair]

Originally Posted by captainwireman

What is it with batteries? I have two that are only topped off once a year in Fairbanks Alaska sitting on my porch that load test strong. 4 years now but they were only lightly used. Yet I keep reading about batteries that often fail prematurely. Is quality control lacking in some brands?

Temperature makes a big difference, a hot climate is much harder on batteries than a cooler place.

[TeddyDiver]

Originally Posted by conachair

Temperature makes a big difference, a hot climate is much harder on batteries than a cooler place.

A thing very often forgotten. Think about a 12v battery with 6 cells. In warm climate the outermost cells have three times more surface area to cool themselves than the rest of them, thus either the first ones get too low charging voltage or the mid ones too high.. Cold regions it could be just the opposite depending of course how the ventilation and engine heat are affecting the bank.

[conachair]

Originally Posted by TeddyDiver

A thing very often forgotten. Think about a 12v battery with 6 cells. In warm climate the outermost cells have three times more surface area to cool themselves than the rest of them, thus either the first ones get too low charging voltage or the mid ones too high.. Cold regions it could be just the opposite depending of course how the ventilation and engine heat are affecting the bank.

Never even thought of that
Love my t105's even more now

[Dockhead]

Originally Posted by conachair

Never even thought of that
Love my t105's even more now

But the same is true of 6v batteries! Just the proportions of "inner" versus "outer" cells is different, but the problem is absolutely the same.

[TeddyDiver]

Originally Posted by Dockhead

But the same is true of 6v batteries! Just the proportions of "inner" versus "outer" cells is different, but the problem is absolutely the same.

In my earlier post I said 2 and 4v batteries are the best in this regard. 6v have an disadvantage but not as bad as 12v as there's only one cell in the middle having cooler cells on both sides. With FLA it's noticeable with uneven water filling requirements between the cells in the same battery. Can imagine what happens with Gell and AGM but dont have any experience about them..

BR Teddy

[ramblinrod]

Originally Posted by TeddyDiver

In my earlier post I said 2 and 4v batteries are the best in this regard. 6v have an disadvantage but not as bad as 12v as there's only one cell in the middle having cooler cells on both sides. With FLA it's noticeable with uneven water filling requirements between the cells in the same battery. Can imagine what happens with Gell and AGM but dont have any experience about them..

BR Teddy

A battery consists of lead, electrolyte, a little bit of electrical insulating mat, and plastic.

As an assembly, it has a thermal mass.

Any thermal mass that generates heat internally (as a battery does) will be warmest in the centre, with a temperature gradient toward the outer surface.

(Assuming the ambient air surrounding the thermal mass is cooler, as would normally be the case.)

If one compares the bulk density of a GC2 6Vdc and a Grp 27 12Vdc battery, they will find them close to equal.

While there are more plastic separators between cells in a 12 Vdc Grp 27, I would suspect the plastic separators in a 6Vdc GC2 to be thicker, with a net result being pretty much a wash with respect to thermal conductivity.

As a result, I don't believe a GC2 has any inherent "cooling" advantage over a GRP 27.

[Cheechako]

Reportedly 6v golf cart batteries have thicker plates. Constant drain and recharge depletes plates faster, so they are designed that way.