dual 6 volt batteries

Sumner · Mar 2, 2012

I see that a lot of guys get them from Sam's Club or Walmart and I priced some at a discount battery store, Batteries To Go I think in Englewood, FL. They had a couple different brands and I think they were around $80. We aren't Sam Club members any more, but will price them there before we buy the ones we need.

Maine Sail on here has a lot of battery info. Do a search as I don't have a link handy,

Sum

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walt · Mar 3, 2012

The ones I bought were Energizer from Sams club for about the price Sumner mentioned. So far so good...

FYI, mine are under the V berth and I only have one "battery" so no 123 switches - except for a combination on/off and breaker as close to the batteries as possible (accessible from the head area). My breaker is 90 amps - sized for 4 gauge wires that run the lenght of the boat to the outboard electric start (draws up to about 50 amps).

Also... there is all sorts of advice about how to make batteries last long - but I think important is to simply maintain the water... I think the main reason my first set got trashed is that I had them in a location that made it a huge and messy pain to add water so I ended up neglecting them.

There is some product for easily adding water to 12 volt batteries (replaces the battery caps) - I should probably look into this for my 6 volt batteries.

jackhararis · Mar 6, 2012

Auto Zone auto parts stores have them.

timebandit · Mar 7, 2012

I have a problem with using two six volt batteries to equal one twelve volt battery.

I would rather wire two deep cycle 12v batteries together in parallel for more capacity than using 6v wired in serries to get 12v.

Why?

If one of the 6v batteries has a failure and I have to remove it from the circuit I will have just 6v and nothing on my boat will run on 6v. Not the radio, lights, gps, depth finder, inverter, engine starter, cell phone charger, not even the anchor light.

I am not even sure I could charge just one 6v battery.

If one of the 12v batteries becomes disabled I can just remove it from the circuit and I will still have 12v to run everything and I can still charge it with the little 6 amp charger on the outboard.

Just a common rotary switch allows this in just seconds.

Just my thoughts.

Don S/V ILLusion · Mar 7, 2012

timebandit said:
I have a problem with using two six volt batteries to equal one twelve volt battery.

I would rather wire two deep cycle 12v batteries together in parallel for more capacity than using 6v wired in serries to get 12v.

Why?

If one of the 6v batteries has a failure and I have to remove it from the circuit I will have just 6v and nothing on my boat will run on 6v. Not the radio, lights, gps, depth finder, inverter, engine starter, cell phone charger, not even the anchor light.

I am not even sure I could charge just one 6v battery.

If one of the 12v batteries becomes disabled I can just remove it from the circuit and I will still have 12v to run everything and I can still charge it with the little 6 amp charger on the outboard.

Just a common rotary switch allows this in just seconds.

Just my thoughts.

That's the hypothesis but consider the practical reaity:

Consider what happens to the "good" 12V battery when wired in parallel with a "bad" 12V battery - they are both depleted equally meaning neither will be useful. I know there are people who advocate for precisely what you suggest but none of them ever dispelled the reality that neither will work in the event one fails.
This seems to be an option advocated by the so-called internet experts.

Maine Sail · Mar 7, 2012

Don S/V ILLusion said:
That's the hypothesis but consider the practical reaity:

Consider what happens to the "good" 12V battery when wired in parallel with a "bad" 12V battery - they are both depleted equally meaning neither will be useful. I know there are people who advocate for precisely what you suggest but none of them ever dispelled the reality that neither will work in the event one fails.
This seems to be an option advocated by the so-called internet experts.

I had a customer who lost ALL the batteries on his boat due to a failure of just one battery. If the internal failure, such as a short, is bad enough, though this is still quite rare, it can take out all the batteries. 12V batteries are more prone to these types of failures as the plates are thinner and buckle and distort easier than do those on 6V battery.

There are lots of boats out there with banks consisting of just two 6V batteries and people save money, get more Ah's in the same foot print, and get longer life due to the thicker plates of a 6V battery than they do with 12V.

In my experience 6V batteries are longer lasting and more robust than 12V so if you can fit them and it makes sense they are a good option. I CAN'T fit them on our boat or I would have them in a heart beat.

I have no qualms about installing dual 6V batteries. Even if there were a failure most boats have a second battery bank and on most boats that is why it's there.

Sumner · Mar 7, 2012

timebandit said:
If one of the 6v batteries has a failure and I have to remove it from the circuit I will have just 6v and nothing on my boat will run on 6v. .

That is true, but what are the odds of that happening. I can't remember ever having a battery experience a sudden failure, but I'm sure there are cases like MS noted. If so how many of us are that far now a days from getting a replacement battery. Even down in the Everglades we were within a day of a battery.

I think the benefits, that MS pointed out, of the 6 volt batteries for us outweigh any negatives. If a person really worried that they might be without an anchor light or something for the night then possibly throw a small motorcycle battery in the boat and keep it charged at home or use the outboard. One of those are less than $40 and would take up very little room. I have one and will probably take it when we switch to the 6 volt batteries. We consider our batteries a safety issue and replace them as soon as they aren't taking a good charge anymore.

Sum

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MrBill_FLL · Mar 7, 2012

The only thing missing from the discussion is trailer sailors vs big boats.

It may be MainSail is on point, that the 6V's are more robust and can take the pounding better.

But I wonder how many using 6V's are on a trailer.

-OTOH, most big boats have a house bank, AND a starting 12v battery, they could use for electronics in a pinch.

(my .02)

fwiw, -I'm running 2) grp27 wet cells fro wallmart.

*EDIT: Sumner are you currently running 2 6V's in the mac?

Sumner · Mar 7, 2012

MrBill_FLL said:
....*EDIT: Sumner are you currently running 2 6V's in the mac?

Not at the moment and probably won't for a year or so as the 2 12 volt batteries are a little over a year old if I remember right. I will change to the 2 6 volts though when these are done.

They are about 3-5 months apart date wise, but both are the same Interstate batteries. We run them in parallel all of the time after Walt pointed out that they charge faster in this mode and then you are using them pretty much the same. If I take one or the other out of the circuit with the switch I do see a couple tenth's difference in their voltage.

I took a rough measurement and feel I can put 2 6 volt batteries where the 12 volt are now. The electric start on the Tohatsu is great, but it will also pull start in case of a catastrophic battery failure or some how we ran them down. So far that has never been the case. We also have backup in that we can/could start the gen-set at any time and of course the panels are also always charging during the day.

If one runs 2 12 volt batteries now I believe that 2 6 volt will give more amp/hr for the buck and are actually more of a deep cycle than the deep cycle 12 volt I have now, and what I think most people have, as they are also 'kind' of a mix between 'deep' and 'start'. Walt has shown that there is no problem starting the outboard on the twin 6 volt setup.

I'll also bet that there are a lot of people reading this that only have one 12 volt battery now and they might not care or have the room for 2 of either voltage batteries. We didn't before, but after thinking about it on this thread, might start carrying that small motorcycle battery when we switch to the 6 volt batteries. We use to take it to blow the Zodiac up when launching, but now have a 12 volt extension cord that will clip on the Suburban's battery posts.

The Endeavour does have 2 banks of 6 volt batteries that are shot for whatever reason and we will have to replace those and review the wiring to see if it is the culprit. It also has a 12 volt 'start' battery like you mentioned. I brought it home to keep it charged and it is under the computer table and powers the ship's computer that I brought home and in fact is what I now use as my home computer. Saves transferring all of my web stuff back and forth between computers and worrying about messing that up with new and old versions of our web pages.

If for some reason we lost all batteries we have the handheld GPS that we use and have SeaClear on two laptops that we could start and plot a course and download to the handheld. It that failed we do have full size charts. We also have a good handheld VHF. So we could survive a complete ships electrical failure except for the anchor and/or running light and I saw lots of people not using anchor lights on anchorages. Not good, but if you had to for one night not the end of the world probably and we have only moved once at night and didn't like that as it was into Boot Key Harbor where we had never been before.

This battery stuff is a good case where there is not an overwhelming argument one way or the other,

Sum

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MrBill_FLL · Mar 7, 2012

what no faraday cage? LOL!

you're a boy scout! always prepared!

Cruiser1 · Mar 7, 2012

Sumner said:
..............So we could survive a complete ships electrical failure except for the anchor and/or running light and I saw lots of people not using anchor lights on anchorages. Not good, but if you had to for one night not the end of the world probably ...............

40 years ago I used to use a $5 kerosine hurricane light half way up the rigging, when at anchor, rather than relying on the mast head light I had - felt a lot safer that way. Still carry a small one in the lazarette these days 'just in case' and find it often comes in handy - cheap, reliable, easy to use.
http://www.primusaustralia.com.au/index.php?p=line&sid=1286335426

Stu Jackson · Mar 7, 2012

Cruiser1 said:
40 years ago I used to use a $5 kerosine hurricane light half way up the rigging, when at anchor, rather than relying on the mast head light I had - felt a lot safer that way. Still carry a small one in the lazarette these days 'just in case' and find it often comes in handy - cheap, reliable, easy to use.
http://www.primusaustralia.com.au/index.php?p=line&sid=1286335426

I use one like it all the time, but not a hurricane lamp, a small fresnel lens light.

Cruiser1 · Mar 7, 2012

Stu Jackson said:
I use one like it all the time, but not a hurricane lamp, a small fresnel lens light.

They look really nice Stu and I gather you can get the same thing with a combined red and green lens - a combined red/green one and a white one would give the perfect emergency nav lights for any boat I guess

.

Sumner · Mar 9, 2012

doehunter said:
...Sumner,
Does your fridge act up at first when you plug it into 12 volts?
Jim.

Oh, almost forgot this was the battery thread!
I wouldn't have thought I would get more capacity from a smaller footprint using 2-6's!
I'm all for that!

I can't remember for sure but I think ours didn't work period or something was wrong when we bought it. I called the company and they had me remove a side panel and it was just a wire that was not connected. I connected it and it has run for weeks at a time with no further problem.

When you say it shuts off, does the compressor stop since it is in the operating range or does it go completely off? I think that it does have low voltage protection on it. You might see 14 volts on the batteries and think they are topped off, but as soon as they see a load if they are bad the voltage could drop a lot. Didn't you install one of those digital volt meters like we have? The key is watching that and seeing what it is before the frig is on, right after it is on before it cuts off. I'd also try and put another heavier load on the batteries and see what happens.

One thing about comparing the 6 volt to 12 volt is that the amp hours you see for one 6 volt battery is the 'total' amp hours you will be getting with 2 in series that are producing 12 volts. The common 6 volt batteries that are close in width and height to a group 27 12 volt are the T-105 and the GC-2. The have amp/hr ranges in the 225-232 amp/hr with a 5 amp load over 20 hours. So 2 of those in series will give you a total of 225/232 amp hours.

The group 27 batteries generally have about an 85-105 amp/hour rating for the same 5 amp load over 20 hours. Since they are in parallel you add the amp/hrs together, so they have a combined rating of 170-210 amp/hour. They are about the same width/height as the group 27, but taller, so make sure you have room in that direction also.

So by going to the two 6 volt batteries you aren't gaining tons of more amp/hr capacity, about 20 to 50, but like MS pointed out there are a lot of other benefits. One is that they will last longer if only drawn down to 50%, but they are designed to be drawn down to 20% so will take more abuse. Also most sources will give a longer life expectancy for the 6 volt vs. the 12 volt deep cycle in the same deep cycle situation that we are with our batteries,

Sum

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Stu Jackson · Mar 10, 2012

doehunter said:
Sum,
On the fridge, it acted like it was shutting down. The compressor and the fan would turn off, but the led readout was still on.
When it was doing the shut down thing I was watching the meter and it was well over 12 the whole time. If I remember right, the fridge had been set to 45 before and I adjusted it back to 34 when I got on the boat, so it was already set to be working. Once it starts and doesn't quit, it runs good.

Have you ever had the fridge checked for refrigerant level? I have this kinda startup issue, too.

Maine Sail · Mar 10, 2012

Sumner said:
One thing about comparing the 6 volt to 12 volt is that the amp hours you see for one 6 volt battery is the 'total' amp hours you will be getting with 2 in series that are producing 12 volts. The common 6 volt batteries that are close in width and height to a group 27 12 volt are the T-105 and the GC-2. The have amp/hr ranges in the 225-232 amp/hr with a 5 amp load over 20 hours. So 2 of those in series will give you a total of 225/232 amp hours.

The group 27 batteries generally have about an 85-105 amp/hour rating for the same 5 amp load over 20 hours. Since they are in parallel you add the amp/hrs together, so they have a combined rating of 170-210 amp/hour. They are about the same width/height as the group 27, but taller, so make sure you have room in that direction also.

Actually GC2 / T105 size golf cart batteries are closer in foot print to a group 24 than a 27.

GC2 / T105 = 10 3/8" Long by 7 1/8" Wide by 10 7/8" Tall
Group 24 = 10 3/4" Long by 6 13/16" Wide by 8 11/16" Tall
Group 27 = 12 9/16" Long by 6 13/16" Wide by 8 3/4" Tall

If we compare the Deka / Duracell brand from Sam's Club

EGC2 6V = 230Ah for 2 batteries
Deep Cycle 24 12V = 150Ah for 2 batteries

The 6V batteries have 80Ah more for two, or nearly an entire group 24 battery...

dual 6 volt batteries

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