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Catalina/Capri 25/250 Sailor's Forums

Catalina 25 Specific Forum

Size of 6 volt batteries

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Deejavue
Deckhand

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USA
11 Posts

Initially Posted - 03/11/2008 : 14:31:35

We're thinking of replacing our bank of two Group 24 batteries with two 6 volt batteries, probably from Costco. Since I won't be out to the boat until this weekend, I can't measure the height of the battery compartment. Does anyone know if the 6 volt batteries will fit in the same space at the 12 volt batteries? According to the specs, the 6 volt batteries are an inch and a half taller. We have a 1989 Wing Keel and the batteries are located under the starboard quarter berth.

Thanks in advance for your help,
Dee Reed
Sacramento, CA
1989 C25 5984 Wing'n It

Edited by - on

gnorgan
Admiral

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USA
563 Posts

Response Posted - 03/11/2008 : 14:37:53

I also would like to put golf cart batteries there in our 89 C25 but they won't fit....I measured awhile ago. I did put them in our 25 foot Airstream just behind the propane tanks. The 'Stream is a 1992 Excella. Two perfect worlds!!!
Maybe if we build a special compartment just to the centerline, taking some of the quarterberth area next to that bulkhead behind the ladder?

Edited by - on

stampeder
Master Marine Consultant

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1608 Posts

Response Posted - 03/11/2008 : 14:43:00

I'll look for a picture of the Mod the PO did.
He removed the bottom rung of the ladder (companionway steps) and replaced it with a battery box. The battery box becoming the bottom step. It looks like a fairly simply mod, and I didn't know it was a mod until it was pointed out to me by the Surveyor.
Also, it seems to me that there are several places you could use for batteries, the Port dumpster being the one that would require the least amount of work to modify.

Edited by - stampeder on 03/11/2008 14:43:36

Deejavue
Deckhand

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USA
11 Posts

Response Posted - 03/11/2008 : 15:37:51

Thank you both for your help and information. Guess the "installing 6 volt batteries" is going to the bottom of my "things still to do list". Folsom Lake finally has enough water to float the boat and we're launching in a week or so.

Edited by - on

Dave5041
Former Mainsheet Editor

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USA
3758 Posts

Response Posted - 03/11/2008 : 19:40:23

Are 6 volts that much cheaper? Just curious, I like having two batteries and won't change. Two 6 volt 100 amp hour batteries are functionally one 12 volt 100 amp hour battery.

Edited by - on

DoubleD
1st Mate

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USA
61 Posts

Response Posted - 03/12/2008 : 07:00:15

There are 6 volts that are the same size as 12v

Edited by - on

Deejavue
Deckhand

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USA
11 Posts

Response Posted - 03/12/2008 : 12:34:36

Dave,

Do you have the name of the manufacturer of the 6 volt batteries that are the same size as the 12 volt batteries? That would certainly solve our space problem....

Dee in Sacramento

Edited by - on

frog0911
Master Marine Consultant

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USA
1349 Posts

Response Posted - 03/12/2008 : 22:39:48

Two 100 AMP six volt batteries must be wire in series to get 12volts. The end result is 12V 200 AMPS. Two 12 or 6 volt batteries wire in parallel equals 12V 100 AMPS or 6V 100AMPS.

Edited by - frog0911 on 03/12/2008 22:42:40

Dave5041
Former Mainsheet Editor

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USA
3758 Posts

Response Posted - 03/12/2008 : 23:29:25

No, 2 6V 100A batteries in parallel is 6V & 200A, in series it is 12V & 100A. Think of it as a single burst in watts: P=IE . P=100x6 . P=600W per battery or 1200W total output; in series it would be 12Vx100A = 1200W. Its like the first battery providing 6V at 100A and the second battery providing volts 7-12 and the attendant 100A. The total power in watts (the product of I x E) or watt hours must always be the same or you are creating energy.

Edited by - on

OLarryR
Master Marine Consultant

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USA
3448 Posts

Response Posted - 03/13/2008 : 05:17:29

I also have an '89 not that it really matters for this discussion but I do not see what the benefit is for getting 6 Volt batteries in lieu of what I would consider the normal route - two 12 Volt batteries which is how my boat is configured. What is the benefit with 6 volt batteries - cost ? I mean how much are we talkin ? For that, you are giving up potentially the benefit of running one battery when at anchor and saving the other in case the first battery runs down - That is if you use the battery switch. In reality, a 2 battery setup without an isolator or combiner , two 12 Volt Batteries are not like having double the power - like an extra battery in reserve unless you always keep them separate and then are able to individually charge without one effecting the charging of the other. Some books/articles cover this subject and believe two 12 volt batteries run in parallel (which is what I always do) turns out to be only about 30% extra benefit out of the extra battery (reserve capacity). But with two 6 Volt batteries, you get no benefit at all - You need to always run them in series to get the 12 Volt accesories to run and then 2 - 100 amp batteries in series never give you more than that or anything in reserve if one battery became weaker than the other.

I guess I do not see why having a 2 battery system is so important to you but having 12 Volt batteries is not ? A 2 battery setup is a necessity when using 6 Volt batteries. But with 12 Volt batteries, you have a choice - use in parallel or individually. The easiest route for a two 12 Volt battery setup is just a wiring thing thru the battery switch and you get perhaps a 30% increase in use if run in parallel with no switching or etc gixmos that separate the two. If you get the extra hardware to separate them, then you get closer to a real extra battery backup but you take a hit in the cost of the initial setup.

By the way, I received a flyer in the mail the other day from West Marine. believe they have a 12 Volt battery on sale starting this weekend for about $65 each. So...what is the cost of a 6 Volt battery...$40 ? Are we talking a total of $130 versus $80 ? I would go the 12 Volt route if the difference between the battery cost is say less than $50- $60. The batteries should last quite awhile especially if you charge them during the regular season...so the extra cost becomes somewhat meaningless spread over a 2, 3, 4 years or so.

What other reasons besides cost would one even think about going the 6 Volt route ? I must be missing something here. Someone needs to educate me on this.

Edited by - on

OLarryR
Master Marine Consultant

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USA
3448 Posts

Response Posted - 03/13/2008 : 06:18:29

Here's some info I found from following website:
http://www.1st-optima-batteries.com/faq.asp
Cut and paste excerpt:
"
17. Are 6V batteries superior to 12V batteries for deep cycle applications?

It's popularly believed that 6 volt batteries are better for deep cycle power applications than 12 volt batteries, but it isn't true. This myth likely developed from the fact that golf carts use 6 volt systems. Because golf cart batteries were the only deep cycle batteries widely available for many years, the best way to obtain good 12 volt deep cycle power was to connect two 6 volt golf cart batteries in series (or more batteries could be connected in a combination series and parallel configuration for higher voltages like 24 volts or 36 volts.) The effectiveness of that approach owed entirely to the design characteristics and quality of the batteries used, not to the fact that the batteries used produced 6 volts.

In reality both 6 volt batteries and 12 volt batteries are simply built from 2 volt cells; if a battery is built with three such cells, it's a 6 volt battery. If a battery is built with six such cells, then it's a 12 volt battery. To make a 12 volt system by connecting two 6 volt batteries in series is to do nothing more than to build a 12 volt battery with two cases and external interconnection. In fact, every cable end connection results in some efficiency loss, so the two 6 volt batteries, because they must be connected by a cable, will be slightly less efficient than the 12 volt unit."

Edited by - on

DoubleD
1st Mate

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USA
61 Posts

Response Posted - 03/13/2008 : 08:12:58

Dee, I don't know the brand name, but I have several on my houseboat. I happen to see the same brand at Sam's recently.

Edited by - on

DoubleD
1st Mate

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USA
61 Posts

Response Posted - 03/13/2008 : 08:21:07

Larry, From the practical size, I have a house boat with 15 batteries on it. The 12v ones last a year, from repeated charging and draining. The 6v ones have lasted four years now and counting. The 6v handle the repeated charging and draining better.

I have two battery banks on my C25. One is 2-6v batteries and the other is two 12v batteries. the 6v run my refrigerator and the 12v run everything else.

Edited by - on

Dave5041
Former Mainsheet Editor

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USA
3758 Posts

Response Posted - 03/13/2008 : 09:33:51

I is like Larry said, if you buy the same <u>quality and type</u> battery it doesn't matter. One 100AH 12V is slightly more efficient and smaller but otherwise the same as 2 100AH 6V. The only difference is whether the connections are inside or outside of the case.

Edited by - on

frog0911
Master Marine Consultant

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USA
1349 Posts

Response Posted - 03/13/2008 : 11:23:03

Never can keep that straight. Oh well.

Edited by - on

OLarryR
Master Marine Consultant

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USA
3448 Posts

Response Posted - 03/13/2008 : 12:28:30

Dave has a whole mess of batteries on the house boat, so...maybe the 6 Volt is a bit smaller and lighter and probably easier to deal with space-wise. Still, I think the excerpt I quoted regarding the comparison to golf cart batteries is appropriate unless we get more definitive info on this subject. If you compare same quality of battery in a 6 Volt to a 12 Volt, then would think that the 12 Volt should not last less long than a 6 volt. I would think it would be the other way around. Still this whole thing just doesn;t make sense to me...think about it:

If you have 2 - 12 Volt batteries, you could theoretically run everything on that one and keep the other on standby charging it a few times to keep it from trickling down. How could 2 - 6 Volt batteries that have to be in series last longer. Let's exaggerate this a bit and say that one of the 12 Volt batteries is not doing so well...it has a bad cell. You still can run everything on the other 12 Volt as long as you did not keep them in parallel for the past few months. But if you had one cell bad on the 6 Volt battery - then you are not putting out close to 12 Volts and will not be able to start the engine even if one of the 6 volts is in stellar condition.

I suspect that comparisons between 6 Volt and 12 Volt with the 6 Volt batteries outperforming the 12 Volt probably have to do with the 6 Volt batteries perhaps premium batteries and the 12 Volt ones of a lower amperage/quality than other 12 Volt batteries.....unless someone can point to an article or some rationale why a 6 Volt makes sense.

Edited by - on

Dave5041
Former Mainsheet Editor

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USA
3758 Posts

Response Posted - 03/13/2008 : 12:43:28

You only need 2 formulas to understand everything in your dc system: PIER

P=IE : Watts=current x volts so I=P/E and E=P/I but we are normally 12V anyway

And

I=E/R : Current=volts/resistance so R=E/I

Add up your amps times hours and subtract from your battery.

If anybody cares by this point

Edited by - on

DoubleD
1st Mate

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USA
61 Posts

Response Posted - 03/13/2008 : 22:15:51

Larry, I have used nothing but 12v batteries for the past 30 years, until I bought my houseboat. I have never had good luck with any 12v battery I used in any boat. I have read a lot of articles about battery use on boats. Since I have had such good luck with the 6v on my houseboat, I thought I would try it in my C25. This will be my first season with them. I agree with your thoughts about the 12v battery having a bad cell and not being about to start your motor, but I will just have to pull the cord if that happens.

A couple of the articles I have read, explained the preference for 6v because they can be drained below their 50% capacity and then recover when charged. Draining a 12v below 50% just ruins them. I don't know what to believe.

Edited by - on

OLarryR
Master Marine Consultant

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USA
3448 Posts

Response Posted - 03/13/2008 : 22:32:11

Dave - I have to think there is something to what you say about the 6 Volt batteries based on your experiences through the years. Maybe it has something to do with the 6 Volt batteries being quite a bit more discharged before being recharged compared to the 12 Volts that perhaps do not go thru such big recharging rates. I don't know......maybe I will look into this some more.

Edited by - on

Doug C.
Navigator

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USA
146 Posts

Response Posted - 03/14/2008 : 00:49:35

I use 6 volt batteries on my RV and am about to go 6 volt in the boat.

The data I've seen and my experience shows that 6 volt golf cart type batteries are much better in systems where lots of deep cycling occurs.

I will be replacing my two group 24 Lifeline batteries. Checking the options yeilds the following;
2-group 24 w 80amp cap @$279 each yeilds 160 amp cap for $558
2-group 27 w 100amp cap @$319 each yeilds 200 amp cap for $638
2-6 v GC w 300amp cap @$301 each yeilds 300 amp cap for $602

I will maintain a seperate motor starting group 24 that will work for emergency should one of the 6v die.

The Lifeline website has some excellent info and load calculators.

Edited by - Doug C. on 03/14/2008 00:50:16

OLarryR
Master Marine Consultant

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USA
3448 Posts

Response Posted - 03/14/2008 : 05:11:32

Doug,

In your case, if the 6 Volts you have used in the past is anything like what you stated in your posting, well then the reason for them lasting longer is they have about twice the amps of the 12 Volt batteries you also mentioned: 300 A vs 160 A. But then again sounds like you will have a bank of each onboard....4 batteries ?

I have very minimal needs for batteries to be such a big deal. So, maybe I should bug out of this conversation altogether. If I were to use 120V at my slip, they would charge me an addl $20/mo and since I have little to run (use a portable mini-boombox w/it's own batteries) and no electric bilge pump/continual leakage like those with inboard/outboard drives, I forgo the electric at the dock.

Similarly, my electrical needs from the batteries while sailing or at anchor are also minimal. I have an LED Anchor light (.15 -.2A/hr) and I recharge the running lights loads or daily battery trickle with my Honda w/12A alternator but mostly with my 20 Watt solar panel. If I am staying as a transient at a marina, I hook up to the electric and then I have a recharger that automatically kicks in when the shore power is hooked up.

I have 2 of the less expensive flooded 12 Volt batteries that West Marine oftentimes sells for ~ $70/ea and the PO had these batteries for a number of seasons before I bought the boat. I now have had the boat for over 2 years and the batteries are showing no signs of quitting. So..I estimate they are around ~ 3-4 years old right now.

If some of you are paying in excess of $500 for a pair of batteries and they do not last all that long and so that is the reason to seek other solutions like....maybe going w/6 Volt batteries because past experience indicated they performed better......I still see some things that don't add up. Youse guys must really need to use a lot of juice seasonly and so tweaking the max out of batteries seems like a bigger deal than I would have thought. A lot of overnighters at anchor using cabin lights and anchor light that are all incandescent bulbs and no solar panel for recharge ? At $600 for a set of batteries, may want to consider a solar panel to maintain your battery investment.

Edited by - OLarryR on 03/14/2008 05:15:20

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