AGM Batteries vs Wet Cell

[hellosailor]

Wheels, the battery maker types tell me that because AGM uses a starved matt, rather than a liquid electrolyte, all else being equal you can always push more amperage into them without getting the electrolyte bubbling and stratifying--and that gives them a higher charge/discharge rate than any wet cell will have. I can't swear by it--but the folks that make them seem to uniformly say it gets rid of the problems with liquid electrolyte.
Whether that makes AGM "better" in the larger picture (less prone to sulfation, incredibly lower self-discharge rates, more expensive, etc.) is another issue. But the more controlled chemical reaction, and lower sulfation, are big points for them.

[senormechanico]

Has anyone ever opened up a bad AGM battery to see what they look like when they're dead/damaged? I'm curious as to what actually physically happens inside when they refuse to take a charge.

Steve B.

[Alan Wheeler]

As far as I understand it, and this is what I have gleaned from Rick, is the main contributing factor to current limit is heat build up. Rick has suggested that very high currents can be used in charging FLA, providing the temperature is monitored and current controlled to suit. I had also learn't many year ago (and maybe incorrectly) that very high currents will also cause plates to warp in starting batteries. These being much thinner plate construction of course. Just why AGM is different is beyound me, but maybe it is something to do with being able to wick away heat faster. Not sure. But one thing I do know, in deep cycle applications, the AGM's just do not seem to last. And with Calcium designs becoming the norm now, we are going to see the cheaper batteries that used to be the norm, much less able to suit deep cycle applications. Here is an interesting problem I had occur. My large Endurant N200 traction batteries used to be recommended as having the ability to deep cycle. One looked like it had failed at 23mths of age. The latest N200 is now using calcium, I guess to reduce cost. But it means I had a delema of not be able to replace the battery with another for deep cycle use. So hence me going for the big new German batteries. Which in the end, worked out close to the same price anyway. The supplier of the N200's was finding more and more batteries are now being made with Calcium and it is starting to cause a hadache for many applications they deal with daily.

[rebel heart]

My vote is standard flooded lead acid. They're cheaper, tolerate stupidity better, and have been around longer (thereby being more durable, in my mind). You also have more options (golf cart, marine deep cycle, non-marine deep cycle, etc). In a pinch, you could go to Sears and have your boat moving again $100 later.

I was in the Navy and worked on electrical gear a lot; I just don't have the energy to care enough to make the AGM thing work for me. Maybe when they idiot proof them I'll pick them up.

[Alan Wheeler]

They're cheaper, tolerate stupidity better,

Maybe that's why I have them :-)

Maybe when they idiot proof

Not possible. There is always an improved model of an Idiot made, closely following the release of the device made supposedly Idiot proof.
Thank God I am an old model of an Idiot. I can rest assured there are worse than me out there now.

[hellosailor]

Wheels-
Apparently when you charge with DC, in a liquid electrolyte you get self-limiting because high amperage will cause microscopic gas bubbles, which increase the resistance, which in turn require more amperage, which generates that excessive heat. As it was explained to me, the starved matt in the AGM batteries (which is only about 90% wetted with electrolyte, it is neither a gel nor liquid but a "damp matt") doesn't form bubbles as easily. No bubbles means you can ramp up the charging power higher without generating the same heat levels. And, faced by a physical barrier instead of a pool of liquid, the lead can't migrate off the plates as easily.

In the wet cell there is also another process limiting charging: The bubbles grow and rise, so the electrolyte depletes unevenly and the plates charge unevenly, with more resistance and less charging (IIRC) at the top of the plates where there will be more bubbling and less heat. Some batteries claim to be specially built so the electrolyte will slosh around more and even itself out faster. But in the AGM? No sloshing, no circulation on the "damp matt", so that problem also doesn't exist.

Of course looking at a black (gray, blue, whatever<G>) box with cables attached to it, they all LOOK the same from the outside.<G>

[camaraderie]

Alan: "Firstly, AGM's will never last as long as an equivilant FLA

First...my comparison specifically stated STANDARD deep cycle wet cells...not specialized, high priced wet cells.
Second...I don't know how you can make such a blanket statement. Did you look at and review the data and charts developed by vonWentzel in my link?? What specific criticisms do you have of his methods or findings?

I think wet cells are the best and most economical solution for most sailors...but based on VonWentzels work and my own experieince with BOTH types in a full time year round, mostly at anchor cruising situation in a LARGE amp/hour daily use situation, I much prefer the AGM's and believe they are better and more economical overall FOR THAT USE.

[hellosailor]

I remember having some disagreement with his conclusions but would have to make time to go back and read them again to see why.

An interesting thing, when you say "most sailors" would you agree that "most sailors" either haul for the winter, or often leave their boats unused for several weeks at some time? (Or are most sailors running >20' and trailering home? Or running actually powerless, on daysailors?)

Most of the folks I know with boats haul them for the winter, or hit times when the boat will be unused for a month at some point. In situations like that--AGM can quickly pay for itself, since it can survive the winter layover without any charging and without any damage--unlike wet lead cells, which will take permanent damage after 30 days of sitting by themselves and sulphating.

Which blanket statement are you referring to?

[Alan Wheeler]

First...my comparison specifically stated STANDARD deep cycle wet cells...not specialized, high priced wet cells.

Hey easy there. I ain't picking fights OK!.

So to answer your question....But is there a "standard" deep cycle FLA?? There is either a true deep cycle, or poor and cheap attempts/alternatives at such. Would it not be true that when we go for an AGM, we are trying to better other alternative? Would it not be true that you like the AGM because you feel it is supperior?, so therfore, would we not be also considering a "true" well engineered FLA to compare against. Otherwise it is not fair apples to oranges comparison. There are mo0st certainly many advantages to AGM. Hence why I use AGM for engine start duty. But there are also many advantages to House duty and hence I do have well engineered more costly FLA batteries for that use. Why? because it is a known fact that AGM does not last as long. I do not have to read somebodies paper on this when we have in residence here the guy that basicaly wrote the book many of these other guys learn't from.

[hellosailor]

"because it is a known fact that AGM does not last as long. because it is a known fact that AGM does not last as long. "
In all the poking around I did last year, I never saw or heard that. Can you cite me any source for that--from a maker or other party?
All I can suspect is that since few makers ever discuss actual plate thickness, and plate thickness is one key indicator of longevity for deep cycles, we've got no real way to make comparisons. (And trying to compare plate materials themselves would be even harder.) Of course if all this was "easy" there would be a simple rating and buying guide out there somewhere, beyond Consumer Reports for car SLIs.<G>

"Would it not be true that you like the AGM because you feel it is supperior?, "
If you define "superior" as "will never ruin my clothing again" damned straight. But I do not feel AGM is superior for every reason and every purpose, never said it was.

[Rick]

On 28-10-06 a review of AGM LA superiority over that of any flooded LA battery was submitted. Since that time the gel-cell, and two Fullriver as well as Optima batteries are performing well. As of this date the Optima is the newest battery being more than 5 years old. The oldest is the Prevailer gel-cel, which is over 12 years old. The Fullriver batteries are now 8 years old.

The whole "key" to keeping AGM and quality gel-cel batteries to perform well is having a good charge regimen applied once they have been deep-cycled. Most batteries are murdered by UNDERCHARGING they are not allowed to die a natural death. To be sure, any lead-acid battery can be overcharged yet it is one's natural conservative self which tends to undercharge batteries given a choice of charge setup values. By using the Amp-hour law and a good battey monitor one can view whether or not excessive charge current is being applied at any time removing self-doubt.

The following is the review:
AGM and gel-cell performance notes
I recently finished a 5-year test on two brands of AGM batteries. One I will not mention because it failed to perform as a high-output inverter load type of battery. At the end of five years standing without a charger upon recharge it developed a shorted cell.

The other AGM is a Fullriver battery (yes, made in China). After standing without a charger (average temperature 20 deg C) for five years it had a terminal voltage of 12.3 Volts and did take a charge to recover the lost self-discharge. Originally this battery (a 4-D case size rated at 200 A-hr: HGL200-12) not only actually tested out at 200 Amp-hours it delivered a real 2.32 kilo-Watt-hour true energy. No flooded-cell 4D that I have tested has ever come close to either the actual Amp-hour value or kW-hr value.

I have not yet tested this particular unit for kW-hour value yet have placed 80 Amp heater loads on it until getting 1kW-hour output and terminating the test when the terminal voltage fell to 11.5V merely to observe internal cell resistance. To be sure, the internal cell resistance grew from an initial 2.3 milli-Ohms to 6 milli-Ohms while standing without a charge yet this unit still performs well, especially since I had expected it to perhaps die a permanent death.

A "sister" of this battery has been cycling along with a 10 year old Pravailer gel-cell as well as an East-Penn Mfg AGM (WestMarine 8A4D). All three batteries are 4D case sizes and are operated in parallel, each one having its own battery monitor to test for charge/discharge "tracking" and other parameters. All three battery brands are performing very well.

One surprise is that the Prevailer gel-cell is exhibiting a degradation from 100% down to 65% performance in terms of internal resistance and ability to deliver/charge accept currents compared with the other "newer" batteries. This particular gel-cell battery has been "hammered" in the lab making various inverter/charger and battery monitor tests and 5 years ago I would have not been surprised to have it die soon. Well it has not. Perhaps this is a support of the claim that gel-cell batteries will hold up to greater and deeper cycling than AGM batteries. Regardless, both types perform very well in my opinion and as long as one pays particular attention to the manner of charging using a "real" battery monitor then one can expect much greater performance than any flooded-cell battery.

Of interesting note is that the Fullriver batteries are specified to function under charging voltages up to 14.9 Volts which, coincidentally (or not?) is the terminal voltage that I have been using (depending upon temperature) to achieve Amp-hour-law charging (see my submission in this section from the archive submissions on this topic) for all of these batteries with the wonderful result of cycle-by-cycle stable and low internal battery resistance. This translates to user happiness with consistent cycle-by cycle battery performance over time.

[johneri1]

There's a guy named Andy in southern Oregon who will answer any question you have about batteries; he is at Motorcycle Batteries, ATV, Car, Marine, and Solar Battery Products | Batterystuff.com. He fixed me up with two golf cart AGM six volts that in series provided 400 amp hours of storage--they outlasted two RVs (although I admit changing RVs like socks) charged with a 75 watt solar panel and high tech controller (quality counts big here). Originally needed AGMs because I wanted the batteries inside--made a believer of me: bought another for my Harley which sits in sub-freezing/sub-zero cold for five months out of the year--never even sounds like it's not going to start. Nothing wrong with lead-acid (especially price-wise) just don't wish to sleep next to them. Happy New Year! Oh yes, Andy distributes batteries via UPS; and no tax. (No I ain't related to him!)

[Rick]

Don't like to keep reminding this point: the term "lead-acid" does not denote flooded-cell constructed lead-acid batteries. AGM and gel-cell constructed batteries are sub-categories of the general "lead-acid" electrochemistry. They are ALL "lead-acid" batteries.

[Therapy]

Originally Posted by Rick

Don't like to keep reminding this point: the term "lead-acid" does not denote flooded-cell constructed lead-acid batteries. AGM and gel-cell constructed batteries are sub-categories of the general "lead-acid" electrochemistry. They are ALL "lead-acid" batteries.

Yea, but us local yokels know when someone says "lead acid" we know it means that if you crack it or lay it on it's side it, will leak that liquidy, acidy stuff that makes holes in things and burns.

[Landshark]

I replaced my four 4-D wet cells with FullRiver AGMs. Could not be more pleased. Two attributes of AGMs stand out. First, the self discharge rate is extremely low. After weeks alone my house bank looses less than 6% of charge (measured with XBM). By comparison wet cells have a very high self discharge rate. Second, the AGMs ability to absorb virtually all the amps I generate is outstanding. I have a 200 amp alternator and recharge times are incredibly short. The wet cells have high internal resistance and high amp charging had negligible effect on reducung the lenghty charging time.

My AGMs have been in service two years. I am very pleased.