12v vs. 2x6v Batteries for Sailboat

[MicHughV]

This is a no brainer.....deep cycle 12v batteries cost an arm and a leg...and maybe some $$ on top of that. Avoid Marine stores, where this will cost 2-3 times more than a regular store. Walmart. Costco, etc, all carry 12v and 6v batteries.

Golf Cart 6v batteries are the way to fly....no question. They cost 1/2 -1/3 the price of a deep cycle battery.

But, the big difference is that the golf cart batteries can be run down and re-charged MANY MORE TIMES than a 12v battery. They have easily 2-3 or times the re-charge capability of a 12v battery.

Beisdes the above stores, most towns have "battery stores" where you can find 6v batteries at a good price. Like the 12v batteries, there is wide selection.

The only downsize to a 6v battery is that it is slightly " taller" than a 12v battery and will not fit in a standard battery box. You need to check the space available where the battery will locate.
I'm not sure of the height difference, but I would guess 2" or so.

Two 6v will give you a good 220 amp-hrs, with many recharge cycles.

[hooligan6a]

If you go with 2-6 volt and one cell goes bad you no longer have a 12 volt system.
If you have 2- 12 volt batteries and a cell goes bad, you still have one 12 volt battery.

[Stu Jackson]

Originally Posted by hooligan6a

If you go with 2-6 volt and one cell goes bad you no longer have a 12 volt system.
If you have 2- 12 volt batteries and a cell goes bad, you still have one 12 volt battery.

For the OP:


We hear this all the time when the question is asked.
And it is absolutely true.
However, part of the answer was in the OP's original question: he has a separate reserve or start bank.
If his house bank fails, he has a backup.


Of course, one would followup by asking if he has either appropriate switching to allow the reserve bank to power limited house loads to get him home.
Or jumper cables, not a favorite choice of mine when a switch would be a LOT easier.
It also sounds like the OP is a local cruiser not far from home or resources.

[hooligan6a]

Yes he will have a start battery but if he uses it for a house bank it is not going last long. Everything will stop working in a very short time.

[john61ct]

Originally Posted by MicHughV

Avoid Marine stores, where this will cost 2-3 times more than a regular store. Walmart. Costco, etc, all carry 12v and 6v batteries.


…
Beisdes the above stores, most towns have "battery stores" where you can find 6v batteries at a good price.

Specific maker and model is very important to get best value.

I have never seen a true deep cycle battery sold at either of those stores, nor automotive sources.

There may be exceptions that prove the rule, but. . .

Those specific Duracell (actually Deka/East Penn), besides Sam's Club, are indeed sold by
BatteriesPlus, also Deka-labeled, same batts also sold at Lowes.

That does not mean other GCs sold at those three locations are suitable for deep cycling usage, i.e. will last many cycles.

The other good quality makers (besides Deka/East Penn) of true deep cycling GCs include: Rolls/Surette, Trojan, U.S. Battery, Crown and Superior.

If you want even better than the Deka GCs - at a higher price of course - best to call the maker directly and ask for their sellers nearby your location, often specialists serving industry, but usually willing to sell to individuals.

Paying for shipping lead in low quantities usually throws the value proposition right out the window.

[john61ct]

Originally Posted by hooligan6a

Yes he will have a start battery but if he uses it for a house bank it is not going last long.

The point here is building a solid House bank.

That will be perfectly fine for cranking purposes, a trivial draw in this case.

Compensating for lack of a dedicated Starter with other redundancy measures is not a challenge, many ways to skin that cat.

Yes if two paralleled 6V strings would fit, that would be ideal in many ways, but in this specific use case would be overkill.

[Cheechako]

Another thought is going to glass mat or gel batteries. Maybe you can fit more capacity. They dont have to be installed right side up.
But one thing: Extra capacity does no good unless you have a way to fill it up. And you dont need more capacity than you CAN fill up or use.

[MicHughV]

I've gone through dozens of batteries in 35 years of sailing life.
I can't recall a time when I ever lost a " cell". The whole battery typically dies, not just a single cell.
But losing a cell can happen, just never happened to me.
The 6v batteries have a much heavier construction than a 12 v battery....I have experienced both, and my vote is the 6v all the way!

Following on this thread, keeping a batter fully charged or near fully charged is the secret to a long life. In this respect, solar panels, wind-chargers, etc, is the secret.
dis-charging a battery below 50% is usually the beginning of the end for a battery.

A good 220 amp-hr 12v battery is a big and heavy beast....easily over 100 lb of weight and can cost several 100 dollars....I've seen prices at around $500 for these animals.

Two 6v batteries can be placed separated from each, so space constraints is not a defining feature and easily half the price of the above..

Here's a good book to read
"The 12 volt bible for boats" by Miner Brotherton"....easy to read and understand.

[Cheechako]

Originally Posted by MicHughV

I've gone through dozens of batteries in 35 years of sailing life.
I can't recall a time when I ever lost a " cell". The whole battery typically dies, not just a single cell.
But losing a cell can happen, just never happened to me.
The 6v batteries have a much heavier construction than a 12 v battery....I have experienced both, and my vote is the 6v all the way!

Following on this thread, keeping a batter fully charged or near fully charged is the secret to a long life. In this respect, solar panels, wind-chargers, etc, is the secret.
dis-charging a battery below 50% is usually the beginning of the end for a battery.

A good 220 amp-hr 12v battery is a big and heavy beast....easily over 100 lb of weight and can cost several 100 dollars....I've seen prices at around $500 for these animals.

Two 6v batteries can be placed separated from each, so space constraints is not a defining feature and easily half the price of the above..

Here's a good book to read
"The 12 volt bible for boats" by Miner Brotherton"....easy to read and understand.

I have had 3 batteries short out a cell in about 40 years of sailing. So it does happen. You can tell because your bank doesn't hold a charge long. Charge the bank.... Let it sit a bit and feel the batteries. One will be hot to the touch... it's shorted in a cell inside. Strangely, all 3 instances were batteries that weren't more than a year or 1.5 old.
Another interesting thing was, 2 of the 3 were big 8D batteries.

[Homer Shannon]

Wow, lots of good information here! Thank you. Just to clarify, I figured that one dead 6v battery would put the bank out of commission. With two 12v batteries, I wouldn't - and don't, one IS dead! - have that issue.

However the little tractor battery starts the motor just fine, so I do have 12v backup, I just can't run the evening lights on it. If all else fails, my engine, a Yanmar SB12, can be started with a crank. I have the crank but I've never actually tried to start it that way.

[a64pilot]

I know of only one brand of true 12V Flooded battery, that’s Rolls.
I think there is one more, but I don’t know it’s name.
Rolls are not inexpensive at all. There are Gels and Lifeline makes an AGM, but he’s stated he doesn’t want to install specialized equipment and will be short cycling the batteries, so that pretty much takes both Gel and the Lifeline battery out of the mix, and Rolls are excellent batteries, but not cheap, nor real common.
Pretty much leaves 6V as his only realistic, readily available and inexpensive option.

Oh, I should have included Firefly as an option as apparently they are an AGM that tolerates short cycling, but they are not inexpensive either, nor are they readily available at the local store.

[john61ct]

Look at the list of quality FLA true deep-cycle makers I posted above, they will have good 12V examples,

Trojan T1275 is an example,

but yes usually not as good value ($ per Ah per year in daily use) as the GC form factor.

Dyno is the other good vendor besides Rolls / Surrette for true deep cycling in BCI automotive sizes like 4D and 8D

[roverhi]

We used two 6v batteries for cruising with a 35 amp alternator, no solar or other way to charge the batteries. We sailed if there was any wind at all and had under 500 hours on the engine after 4 years of cruising and bouncing around CA marinas. Doubt that the GC Batteries ever received a full charge let alone reached float level except in the very occasional times we were tied to shore power. They lasted 4 years which is pretty damn cheap electricity for the abuse they took.

You do need to check the fluid levels regularly as letting that get too low is quickest way to kill them. I've switched to remote fill set ups on both my boats not so much as I can't get at the batteries as it's so easy to keep the level topped off. Attach the fill bulb to the remote fill setup, stick the other end in a bottle of distilled water, pump the bulb a few times till it won't pump anymore and you're done. No spilled battery acid, water, and your done in a minute or two. https://petesgolfcarts.com/brands/pr...tering-system/

AGM batteries are good if they are regularly fully charged but that's seldom the case on a cruising boat. Yes, if you have a generator and are willing to run it constantly, an over abundance of solar panels or run the engine every time sailing speed drops below 6 knots you might keep them happy. In the long run, chronic partial charging kills AGM's and negates any advantage to using them other than if you have to mount them on their side or upside down and they are damned expensive.

As someone pointed out, GC batteries are an inch or two taller than regular group 24/27 12v batteries so may need new battery boxes or not fit in the current space.

[TrentePieds]

Homer:

Your Profile sez you are in Wyndham, NH, so I assume you are in a marina, and therefore have access to shore power, as do I where I am. I get along famously in a 30-footer with a dead simple electrical system on two 27 series FLA "fake" Deep Cycle batts. 40A alternator, but no "modcons" such as water makers or fridges or other power gluttons, and, of course, all LED lighting. It works for me because I spent the money on a GOOD "smart" battery charger that keeps a better eye on my batts than I can most of the time, i.e. when I'm alongside and plugged into shore power. The charger "massages" the batts appropriately.

If your boat, like mine, spends a major proportion of her time alongside, whether "at home" or away, this may be your optimum solution to your "problem". I start off the house bank, and when I'm away from my home slip I observe a strict energy budget. Via the 4 position battery control switch I observe the venerable "#1 on odd dates, #2 on even dates" protocol.

The batts live under the navigators seat. You can argue about ventilation, but with SOUND batteries the normal cabin ventilation, in this case the companionway hatch immediately above, does the job. Battery maintenance tools (wrench, terminal cleaner, screwdriver for lifting the caps, hydrometer and Occam's Razor) live in sockets within the box.

Batteries are IMO "consumable supplies", and I change them every four years. Just part of the cost of maintenance.

TrentePieds

[MicHughV]

this is a murky area...

A starting battery is not the same as a " house" battery..
A starting battery needs to deliver a lot of oomph for a very short time.
A house battery needs to provide less oomph but for much longer periods.
The double 6v setup is perfect for the " house system, but for the engine starting battery I would suggest a 12v battery.....
The size of the engine generally decides the size of the battery. Starting batteries use a different way of determining available power.

In case of the house battery...more is always better.....
for instance , say you burn 50 amps a day, and you have a basic 115 amp hr battery....that would be sapping 50% of the battery.
If you had two 115 amp batteries, that would be only 25% of battery capacity.
Ad infinitum...

There's more....get a good battery charging system/monitor that is capable of charging multiple battery banks simultaneously. Batteries need different charging volts...bulk..float..etc...
The same applies to the alternator charging from the engine. A whole chapter could be written on this.

It's a very complex science.....and modern-day digital chargers have come a long way to address these issues......

The modern 12v battery has also undergone numerous advancements...albeit at a price, and not all charging systems are compatible with all batteries.

Having said all that, using two 6v batteries provides, probably, the best bang for the buck for the " house" !! Off course, four 6v batteries is even better.