12 volt vs. 6 volt batteries

Howdy,

I have a 2006 Jayco Jayflight 31 BHS.  It is currently equipped with 2 12 volt deep cycle batteries.  They are pretty much spent ( dealer gave me wrong info on how to disconnect ) and I want to replace them before my next dry camping run.  I just read somewhere that it is better to run 2 6-volt batteries in series than the 2 12-volts in parallel.  With the 12 volts I was planning on installing a switch so I could disconnect both, use one or the other or use both.  I figures I could run off one battery until it was depleted and then switch over knowing I was halfway done, kind of like my dual propane tanks.  But it would be a lot simpler  to run 2 6-volts with a single cut-off switch, although giving up the "backup" battery.

Any thoughts ???

Thanks,

Dan Walker

Dan,
There's a big difference between running down a propane tank until it's empty and similarly running down a battery; a propane tank won't be damaged, but a battery surely will. The rule of thumb with deep-cycle rv batteries is not to run them down below 50% charge. Frequent deep discharges will shorten your battery life quite a bit. If you have the room, you might want to install four 6volt golfcart batteries in a series/parallel hook-up. If not, get a couple of true 12 volt deep-cycle batteries, flooded cell or AGM's - not the so-called RV/Marine deep cycle batteries which are, at best, a compromise between a deep cycle and starting battery. The cutoff switch is normally used to disconnect ALL loads when you put the trailer in storage; not as a nighttime battery disconnect. Just make sure you shut off all unnecessary loads before you turn in for the night, leaving your CO and propane detectors operating. Most smoke alarms use a self-contained battery, so that shouldn't be a problem.

As to the question of running two 12 volt or two six volt batteries

In the RV world there are not six volt batteries

There are only 12 volt batteries

Some come in one piece, some in two pieces but they are all 12 volt batteries

How can I say this?  Simple  There are no 12 volt batteries either, there are only 2 volt batteries

A Six volt golf cart battery is really 3 2 volt batteries in series  A 12 volt is six of them

If you take two six volt Golf cart batteries and hook the POSITIVE of just one to the NEGATIVE of the other. You have a 12 volt  battery. it's that simple, Think of this pair as one battery, treat it as one battery with only two exceptions and all your questions are answered.

The two exceptions: Cleaning (Clean all 4 posts, not just the two at the ends)  Lifting (When you lift them you first disconnect them, THEN you have 2 six volt batteries)

Now: This brings the quesiton "Why do folks say 2 six volt are better?"  Tradition of course.

Not all that long ago you had your choice of 3 classes of batteries

Starting (Could be found in six volt, or 12 volt)

Marine/Deep cycle (I'm not sure if they came in six but they sure come in 12)

And TRUE DEEP CYCLE, which came in Golf Cart and Fork lift sizes.  Golf cart are six volt and can be lifted by a healthy person, Fork LIfts are normally 12 volt by over 1,000 pounds and can be lifted by another fork lift.

Today, you can get True Deep Cycle in different sizes from small enough to fit in your pocket to large enough that you need a fairly LARGE forklift, but it will run your car 300 miles between charges.

You can also get a lot of different chemistries  Flooded wet (Golf cart are usually),  Maintenance free, AGM, GEL and more

But there are still the 3 main classes    Here is the chart

Starting                              Marine/Deep Cycle          True deep cycle

Lots of Cranking amps                                              Lots of Amp Hours
Not so many Amp Hours                                            Not a lot of Cranking Amps

You will notice that the Marine type is not a lot of anything

alfapwr said:

Howdy,

I have a 2006 Jayco Jayflight 31 BHS.  It is currently equipped with 2 12 volt deep cycle batteries.  They are pretty much spent ( dealer gave me wrong info on how to disconnect ) and I want to replace them before my next dry camping run.  I just read somewhere that it is better to run 2 6-volt batteries in series than the 2 12-volts in parallel.  With the 12 volts I was planning on installing a switch so I could disconnect both, use one or the other or use both.  I figures I could run off one battery until it was depleted and then switch over knowing I was halfway done, kind of like my dual propane tanks.  But it would be a lot simpler  to run 2 6-volts with a single cut-off switch, although giving up the "backup" battery.

Any thoughts ???

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Yeah, we are talking deep cycle house batteries here not starting batteries.   You do not need a reserve battery in house applications, your concern is with long term drainage, not ultra high amperage bursts of power to a starter motor turning an engine over against compression.    Do not bother with isolating house batteries, it would be counter-productive -- all you suceed in doing is isolating one battery from the charger and creating a differential state of charge and internal resistance.   If you would use a manual switch over, you also stand a good chance of draining a battery too far (over 50% of capacity) shortening its life.

Hook your 12V batteries in parallel (+ to +;  -- to -- ) or use  two 6V batteries hooked in series ( + to -- ).    A cutofff switch for the entire battery bank is desirable for storage, to eliminate the drain of stray loads like the propane detector.   For that purpose, I like the marine OFF/ON battery switches like those made by Perko -- they are sparkproofed which is handy if they are mounted near the propane tanks. 

Alfapwr did say in the beginning he does a lot of dry camping. I think in general most would agree that two sixes in series would be better than two twelves in parallel for that purpose. Of course weight and room permitting the ideal setup would be four sixes in series/parallel.

Just to keep the record straight, a BATTERY is a series of individual CELLS connected in series inside the same container. A battery can be ANY multiple of an individual cell's voltage. Six 1.5 volt cells in series in the same container would be called 9V battery - think smoke alarm. Similarly, three 2.1 volt acid-type flooded cells in the same case would be a 6 volt battery (we drop the .3 volts in normal parlance for simplicity), and six of them would be called a 12 volt battery (again dropping the odd .6 volts).

I think in general most would agree that two sixes in series would be better than two twelves in parallel for that purpose.

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There is nothing magic about the sixes vs the twelves - the magic comes with the true deep cycle vs the starting/marine battery. The erst of it is in the case size, which translates directly to amp-hours.  But in most areas it is probably easier to find 6V true deep cycles (golf cart batteries) than to find 12v true deep cycles, of which only a few are made (Trojans (flooded or AGM) and Lifeline AGMS are the two that come readily to mind). A pair of Group 27 Trojan 12V deep cycles will perform as well as a pair of 6V golf cart batteries in this application. A pair of Group 30 Trojans would outperform the gold cart 6V's - about 10% more amp hours.

Hi y'all,

Well I learned a lot.  I didn't even consider the differential charging problem.  That takes care of that problem.  I was just looking at the batteries at Sams club.  When I go back I'll check to see if the 12v models are TRUE deep cycle.  If not I may get two 6v golf cart batteries and hook them up in series with a single cutoff switch.  Any good sources for the Trojan or Lifeline batteries ?

Thanks,

Dan

BigEdW said:

Alfapwr did say in the beginning he does a lot of dry camping. I think in general most would agree that two sixes in series would be better than two twelves in parallel for that purpose. Of course weight and room permitting the ideal setup would be four sixes in series/parallel.

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I disagree,  230 amp hours is 230 amp hours, don't matter if you get there by hooking sixes in series or 12's in parallel 230 amp hours is 230 amp hours.

As I said, there are no 12 volt batteries, there are not six volt batteries, there are only 2 volt batteries,  They come 3 or six to a package.

alfapwr said:

Hi y'all,

Well I learned a lot.  I didn't even consider the differential charging problem.  That takes care of that problem.  I was just looking at the batteries at Sams club.  When I go back I'll check to see if the 12v models are TRUE deep cycle.  If not I may get two 6v golf cart batteries and hook them up in series with a single cutoff switch.   Any good sources for the Trojan or Lifeline batteries ?

Click to expand...

Yeah, their websites.  Trojan at http://www.trojan-battery.com/index.aspx and Lifeline at http://www.lifelinebatteries.com/.  Search them for a convenient dealer.

Any good sources for the Trojan or Lifeline batteries ?

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Last year I added 2 more Trojan T-125's to the existing two. Bought them at Gander Mountain for $99 each; cheapest I could find at the time. You might try other large sporting goods stores, as they're used for trolling motors.

Not a source for batteries: But rather leads.

Have a chat with the maintenance manager at your local GOLF COURSE

They are, after all, Golf cart batteries.

More battery questions for a newbie.

Our MH has 2 Interstate DCS-75BT, which I believe are true deep-cycle AGM 12V batteries (please correct me if I'm wrong).

If I understand correctly, these batteries are rated to 75ah @ 20hr so I should have 150ah total.  If I understand correctly, deep-cycles shouldn't be drained to more than 50% and even 30% is recommended which means that in real world terms, when living off batteries, I'm looking at using 75ah max and really using 50ah or less would be best before recharging.  Is this correct?

I believe our batteries are probably not in the best of shape (I think the MH (which we bought used) may have been sitting for several months and the batteries were probably drained and not recharged regularly).  If I were to replace them with 2 6V T-125s, that would give us 240ah at 12V (2x 6V in series) which would give us 120ah max (and should use 80ah or less).  Is this correct?  I kind of prefer sticking with AGMs but if I can get longer life / better performance from the T-105s or T-125s, maybe I can put up with a bit more maintenance (there seems to be mixed feelings on the AGMs).

Is this correct?  Am I missing something?  Is there anything I can do to 'revive' our current batteries (they are about one year old but it seems that they'll drain within about 3 days when we store the RV and according to the 'display panel' won't recharge fully (after I disconnect from the generator or AC or driving), I don't think they'll ever show more than 3 out of 4 lights)) (I checked the RV and other than CO, LP and smoke detectors, there doesn't seem to be any load on them).  Probably even sillier question but how do you check batteries?  I've heard people say that you have to charge them and put a load on them but I don't even know what that would mean or how I would do that - when people say 'battery holds charge', what does that mean and how do I check that?  I saw some mention of 'equalization' - is that something I should do?  I should also mention that I'm just using whatever charger came with the MH (94 AllegroBay) (I don't have an inverter (yet)).  I am under the impression that the 3-stage chargers that come with inverters are better than the charger I'm using - is this correct?

michelb said:

Our MH has 2 Interstate DCS-75BT, which I believe are true deep-cycle AGM 12V batteries

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Yes they are. See the Interstate Battery web site.

The rule of thumb is to not regularly disharge below 50%, although doing so occasionally won't damage the battery.

A pair of T-105s will give you approx 220AH capacity when wired in series for 12 volts. I'd think you could count on 110AH, but this will fall off over time. As I think you know, the T105s are wet cell batteries.

There are mixed opinions on equalizing AGM batteries and I personally only equalize wet cell batteries. It usually results in a noticeable increase in available battery capacity if I haven't done it for a while. But check the manufacturer's recommendations. Of course, you'll need to have an equalize option on your charger.

A load test is the only true battery test. They sell load testers specifically for that, but most auto stores or battery shops will run the test for you. Other indicators are battery voltage and, for wet cell, specific gravity of the electrolyte. Over the years, I've heard/read every argument why all three of the tests are not valid.

Tom

I have a sheet from Lifeline and they recommend equalizing once a year; 15.5 v for 1-3 hours.

Thanks Bernie. Some manufacturers recommend equalizing AGM batteries and others don't. I've never equalized my AGMs and, to date, they don't appear to have shown the loss of capacity over time. Given the two things equalization is supposed to do (see here), I'm not surprised by what I've experienced.

I stick with my advice to follow the manufacturer's recommendations, irrespective of what I do personally.

Much safer to follow manufacturers recommendations after all they designed and built the batteries.

Ron said:

..... after all they designed and built the batteries.

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Maybe, maybe not Ron. There are a limited number of companies who manufacture batteries and many more who market them as their own.

Tom said:

Maybe, maybe not Ron. There are a limited number of companies who manufacture batteries and many more who market them as their own.

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Tom

Even tho a company may, or may not, manufacture the batteries under their nameplate, Lifeline apparantly has full control over the product regardless of who produced it. I talked to the Lifeline president at an FMCA convention about equalizing, since I had heard about not equalizing AGMs. His comment was as I mentioned and he gave me the sheet that gave the equalizing specs.

Bernie,

As I've said several times, follow the manufacturer's recommendations.