Just switched to two 6V batteries: amazing results

[bryanl]

re: "To complete the picture, factor in the battery’s internal resistance" -- That is what makes connecting two batteries in parallel 'share the load.' The voltage relationship to state of charge is one way this internal resistance is expressed.

Issues of self discharge are only at issue out of the context here. As I understand it, we are talking about batteries in reasonably active use, not batteries stored without any proper maintenance for periods longer than a week. Self discharge is only an issue if you have batteries of significantly different age or of somewhat different type (sealed versus wet cell, for instance) setting without any activity for quite a while.

re: "it is not at all a fact that state of charge is related to voltage alone as suggested above."
Again, context. We are talking RV's here and a level of precision appropriate to typical battery use in that context. We need to avoid the 'reduce to the absurd' logical fallacy if we want to learn anything useful.

Specific gravity and voltage versus state of charge charts are quite common on the web. I do know that voltage, like specific gravity, needs to be properly measured. One of the more interesting websites on this topic is SmartGauge Electronics - battery metering as that device depends upon matching current and voltage curves to determine state of charge in a dynamic environment (he's got some very good tech notes on battery bank wiring and configuration with explanations as well). Most of us have to let the battery get to a rest state to obtain reliable measure.

I found I had to do that to avoid overcharging the AGM's.

That is one caveat with using AGM's in an RV. Like other sealed battery types, they are sensitive to overcharging. That often means no equalizing (which most RVers don't need to be concerned about anyway due to their use patterns) and also the storage float levels need to be carefully matched to manufacturer's recommendations. AGM's are nice batteries and can provide an extra year or two of life over wet cells but they should still be in a properly vented battery box and they do need some care about charging voltages. The Lifeline series has become much more tolerant of RV charging systems than they used to be from what I can tell, which is nice.

no slow charge was necessary on Lifeline batteries;

Another nice feature of AGM's - low internal resistance. That can be handy when using inverters as well. But keep in mind that trying to get large currents into a battery to charge it means a rather high charging voltage and that may not be good for other things connected to the battery. Also keep in mind that even AGM's will still need 8 to 12 hours to charge fully, even if you do a high current bulk charge phase. It is that last five or ten percent that take time and it is that last bit that can make a big difference on your battery life.

Any battery charging that runs in excess of 20 amps for every 100 amp hours of battery needs a charger with a temperature probe and the smarts to avoid thermal runaway. That usually isn't an issue in the typical RV setup because, even if the converter/charger can supply the current, it won't run the voltage up high enough to provide that much current for more than a few minutes.

re: "He told me there would be absolutely no problem as long as they were the same manufacturer and the same vintage of battery." -- did he tell you what the problem was if you used same type but different manufacturer or perhaps batteries whose age was a year or two apart? That is what is hard to define, just what the problem really is and its impact on what you want to do. Unless you get to extreme cases or absurd levels of precision, that 'problem' is not of much, if any, significance else we couldn't charge our trailer batteries from the tow vehicle.

[richie rich]

I have a 12v deep cell battery.It is 8 years old.It provides enough watts to power a 12v light so I can read a Zap comic book at night.My portable radio has two AA batteries.The hot water and heater are LP gas.The 6v set up is a great idea,but chances are if I had all that reserve power I would forget to come home.Call me Old School but I like camping the simple no hassle way.I wasn't there, but I hear poor old Wally didn't even have a BIC lighter and traveled the world!

[Buttercup]

Bryan,

I guess maybe we could title your post "I reject your reality and substitute my own".

What you post still ignores the concept of Internal Resistance of the each individual battery when connected in series or in parallel and offers only a simplified DC view of electricity /electronics. And your post still denies the basic complications one can face if connecting old batteries with new ones or when connecting batteries of differing capacities.

rustyrivet - if your vendor states that you can connect these batteries together, it is because he knows that they are matched electrically enough to work together. And if he says its OK - it is as good as you can get, no?

[bryanl]

I think the ad hominem is inappropriate, uncalled for, in volation of the TOS here, and shows an inclination towards anything but trying to understand either what others are saying or anything about the topic at hand.

Making claims about Truth and about others' ignorance is not a good way to engender learning or forward the stated goals of these forums IMHO.

A key issue here, I think, centers on the assertion that voltage cannot be used to indicate a battery state of charge. As I noted, nearly every website with battery information has a table that shows voltage versus state of charge. The battery status indicators in Airstreams are simple voltage indicators. It is something that anyone off grid for a while can measure for themselves. To call all of these websites and the applications of the information in them as a 'rejection of reality' begs many questions.

The facts are, the reality is: That all of us who charge our RV's when we hook up and head down the road connect dissimilar lead acid batteries in parallel; That lead acid battery charging and state of charge estimation in modern systems is voltage driven; That there are many who parallel lead acid batteries with significant differences and do not suffer as a result; That old batteries express the same voltage changes as new ones, just faster.

For reference see "Sealed Lead Acid Batteries Technical Manual" by PowerSonic for a good rundown on discharge versus voltage. -- "Lead Acid Battery State of Charge versus Voltage" by Richard Perez. Perez has a number of good articles related to this topic in Home Power Magazine that are well worth study. I also suggest doing a bit of research on conductance testing of lead acid battery status and finding one of the student papers on the electrical model for a lead acid battery and considering its behavior in various circumstances.

Note that I do not address any particular individual. I do not make blanket unsupported assertions or allegations. I provide references that can be pursued to help see what I am talking about. And I provide examples of the concepts that we can all use as a reference for the points I am making. These are the sorts of things any 'corrections' to my views need to accommodate for me to give them credence. Just telling me I'm full of it doesn't cut it. I need to know how an alternative point of view fits with these things and does so better than the understanding I have.

I provide plenty of material, citations, and examples to address. I suggest it would be more profitable for all here if they were refuted rather than me.

[rustyrivet]

Buttercup, I was not attempting to reject Bryanl's science or impugn his sources. My only reason for commenting was to say there are other sources of information available. When I got my A/S two years ago it only had one series 24 battery, located on the A frame and there was no room for a larger battery. I researched batteries on-line, decided that the Lifeline looked like the best battery, regardless of price. I contacted a local RV Shop (Blue Lake RV) and spoke to Lars. I told him I wanted to add another battery. He determined that, if I used a Lifeline battery, I could put it in an inside compartment and that it would be safe to do so without venting to the outside. He also said the compartment was large enough to accommodate a series 27 battery, which would give me slightly more storage power. I had read articles on line that said you should not mix sizes. To get reassurance that it would be OK, I called Lifeline and spoke to Justin. He said that as long as the batteries were both Lifeline and of the same age (in my case, new) there would be no problem. I had the batteries installed on the basis of those conversations. I figured that Lifeline must have some of those EE types working there, and unless there is a complete disconnect between their engineers and their customer service folks, I should be all right. I did put the inside battery in a sealed battery box and vented it to the outside. As an added precaution, I just switched my converter to a PD 4655. So far, no problems. I will keep you posted if they occur. I make no pretense that I understand electricity: AC or DC jc

[istoilkovich]

Aolani, can you verify which batteries you installed? I am doing the same conversion because my oem interstate batteries stopped holding a charge after about 6 months (2009 Airstream 27FB) probably get better results from a couple of AAA's at this point. My stock battery box is approximately 10" deep and the Lifeline AGM's I am looking at are the GPL-4CT's which are 9.92" tall and with the cables will require an additional 1" of clearance (similar to your mod). You indicated that you put in the GPL-6CT's which are 12.94" tall, which would require about 4" of clearance, was your battery box deeper to start with? I would like to put as big a battery as possible, any clarification will really help.

Just for the record, I think the performance difference between the stock oem batteries vs. the Lifelines sound pretty amazing, I would be stoked to get similar results, regardless of the hair splitting contest that went on in this thread. Thanks.

[2airishuman]

IF u need help visualizing the box mod,

there are several threads WITH PHOTOS of this in post #16 above, so check out those links and pics.

and it's NOT hair splitting.

install HEAVIER/larger batteries and EXPECT more amp/hour reserve and useful capacity.

it's not amazing OR hair splitting, it's simply MORE lead and acid in a bigger box.

ya know how the trial size deodorants don't last as LONG as the family size BIG stick?

same thing same thing...

cheers
2air'

[istoilkovich]

No, I am clear on the box mod, it's more of a math question, 10" stock battery box + 1" mod = 11" clearance, try to put a 12.94" battery plus cables in an 11" box = doesn't fit. And I think your missing the point on the word 'amazing', when you go from barely getting through the night with your batteries to lasting 3 days, it's amazing. The physical size of the batteries is not drastically different and I realize it's a simple concept that yields the better performance, but sometimes you get excited when something works.

[2airishuman]

not missing anything here.

it's NOT possible that 'barely one night' becomes 3 nights...

not with the change as described.

it's simple amp hour math and the EXTRA WEIGHT give more juice...

but NOT 3 times more juice, THAT would be amazing.

and there is NO PERFORMANCE DIFFERENCE that is not accounted for my MORE lead and acid and water...

heavier=amazing, 2x6v vs 2x12 has got nuttin' 2 do with it...

except the 2x6v WEIGHS 180lbs and the 2x12 weighs 120 lbs.

once again the battery box mods are CLEARLY posted in other threads and with a LOT more credibility.

i do agree that occasionally when MORE money is spent for MORE WEIGHT and something good happens it can seem amazing.

cheer
2air'

[richinny]

a good battery, replacing a bad battery, is always an improvement!

[hshovic]

Hi,
Two years ago I made the 6v switch.
Works like a champ.

Battery tales – upgrading batteries for boondocking Safari SE - Airstream Forums

[Aolani]

Istoilkovich -
Sorry for the delay replying; was out enjoying Life (smile). Am pretty sure I ended up with the GPL4CT (would have to go check- it's been awhile). They fit into the factory box perfectly from a width/length perspective, but were of course just under 1" taller, as predicted.

My heighth extension modification shown in one of my initial posts was just about 1".

We still love the improved results and have boondocked quite a bit. Even spent two weeks boondocking in the spring up at Burney Falls with moderate sun hitting our solar panels. Used our genset occasionally, mainly for TV and to top off the batteries every few days when no real sun at all (unusually cool/cloudy spring this year here).

The system of better battery performance/capacity + solar worked great. We're happy and pleased we made the investment (we boondock a lot).

Good Luck!

[toddster]

So, I'm thinking of getting new batteries for my '67 GlobeTrotter. Should I get 2 12V in parallel or 2 6V in series???

Kidding!!! Please do not respond to that question.

My only observation is that after adopting one form of multiple battery religion, I may have to switch sides due to physical limitations. Isn't life grand. I guess either way, the added capacity of a second battery is something I like to have!!!!. Happy trails my friends, I have REALLY enjoyed reading this discussion.

One side note about energy storage.... Back when I worked as an engineer at Tesla Motors, the Roadster's battery pack was rated at 53kW-hr capacity. How I would love to boondock with that sort of energy in reserve.

[ostream]

Originally Posted by Aolani

The system of better battery performance/capacity + solar worked great. We're happy and pleased we made the investment (we boondock a lot).

Good Luck!

Thanks for sharing! We did the a similar upgrade and are experiencing great results. We went with (4) Lifeline 6V's, plus solar and have effectively removed energy management from the list of things to worry about while boondocking.

[27fb2freedom]

Originally Posted by 2airishuman

with 2 batteries i consider 2x6v as NOT an improvement and with the potential for NO juice


1 can also buy/use one GIANT 12v agm (like the 250LB offering from lifeline) and that's another ok approach.
here.

I dont get this one of your main reasons to avoid 2x6v is reliability/duplicity incase of a single battery failure the other 12v can take over by itself. One big 12v losses this advantege?

[ROBERT CROSS]

Originally Posted by ostream

....... list of things to worry about while boondocking.

What's to worry when "dock'n"....seems like a waste of time.
Just do it...

Bob

[Inland RV Center, In]

Originally Posted by 27fb2freedom

I dont get this one of your main reasons to avoid 2x6v is reliability/duplicity incase of a single battery failure the other 12v can take over by itself. One big 12v losses this advantege?

The real idea is to use 2 12 volt batteries instead of 2 6 volt batteries.

With the 12's, one can fail and your still in business.

With the 6's, when one fails, your "OUT" of business.

Andy

[tpi]

I stumbled into this thread from a google search for the batteries I'm installing in my motorhome. The Lifeline GPL6CT.

I think the mod the OP did was excellent, and it was lost in a lot of ridiculous static on this thread. Very much unlike what's typical on this forum.

He doubled the amp hour capacity in the battery box. The GPL6CT are 300 amp hours, the two group 24s are about 150-160 amp hours. It is a huge and dramatic increase in amp hours.

I would hope this post gives this mod a bit more exposure. On my motorhome I'm upgrading from GPL4CT to the GPL6CT. About thirty percent improvement.

This guy's mod is a heck of an improvement with little cosmetic change to the trailer if indeed the post is correct he used GPL6CT. I would consider added bracing, if necessary, to accommodate increased weight.

[Scott J-24]

So, the battle continues between two 6v batteries in series vs. two 12v batteries in parallel....

[tpi]

Originally Posted by Scott J-24

So, the battle continues between two 6v batteries in series vs. two 12v batteries in parallel....

Why should there be a battle? Both configurations are very successful. If the 6 volt configuration can squeeze more amp hours into a space due to battery dimensions why not consider it? Or vice versa for that matter.