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Old 28-10-2006, 15:55   #1
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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.

Thought you-all might want to know about some of these performance results.

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Rick
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Old 28-10-2006, 16:09   #2
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Old 31-10-2006, 20:15   #3
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Thumbs up nice info

Quote:
Originally Posted by Rick
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.
Nice info Rick. I'm not sure if I read this correctly. You actually left a battery for five years without charging it and it still read 12.3 volts? I'd have thought the battery would be dead.
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Old 01-11-2006, 12:19   #4
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Yes, it went uncharged for five years!

I kept checking it every 6 months or so thinking of a similar test that was made several years earlier with a Prevailer (which also held up in a similar manner for over 3 years....just didn't wait the 5 years for that test). I just wanted to know the comparison and I had the extra two batteries to make the test.

The good quality gel-cel and AGM batteries are made with very pure elements in just the right amounts to obtain such low self-discharge values. Obviously the time of self-discharge varies (not necessarily linearly) with temperature.

By comparison, flooded-cell constructed lead-acid batteries, even the best ones, are quite crude and relatively "contaminated". By their nature they are, in fact, somewhat self-contaminating generating shorter and shorter self-discharge times with age.

I've believed for several years now that the main reason more people are afraid of going cruising with gel-cell or AGM batteries is due to the lack of understanding that the entire charging system must use gear appropriate to the battery types and even battery "people" themselves (who traditionally "know" only flooded-cell types) are relatively ignorant regarding the textbook knowledge regarding the care and treatment of the better battery types. As such, the gel-cell and AGM batteries have received a bad rap due to their premature demise due to mistreatment and ignorance.
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Old 01-11-2006, 13:32   #5
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I would have to agree with you on the reasons AGM's get a bad reputation. It ain't magic. You still have to do things right no matter what you use.
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Old 01-11-2006, 13:53   #6
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Rick,

I have heard that AGM's aren't suitable for cruising because of the way most cruisers use batteries, namely, running them down 50% before charging. The anecdotal evidence is that AGM's don't take kindly to that and fail prematurely. Now most of the boats I've talked to have smart chargers and smart regulators yet this is the knock on AGM's. There is no similar complaints about gels. The only caveat on gels, it seems, is not to exceed the maximum allowable voltage when charging. Do you know why this is happenning with AGM's?
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Old 01-11-2006, 19:34   #7
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Most batteries are killed by undercharging

Yes, to be sure, there are the cases whereby a non-regulated charger "kills" lead-acid batteries (all kinds, flooded-constucted, as well as VLRA) due to either over charging or undercharging. Most batteries in the service of cruising boats are killed by UNDERCHARGING (NOTE THAT I DID NOT SAY ALL, MERELY MOST).

AGM batteries are not as tolerant as are Gel-cell batteries for very deep continuous cycling (beyond a state of charge of 50%) yet they DO tolerate that. Here's the deal; Because all lead-acid batteries (yeah, I realize that many of you out there think that there is actually a difference between lead-acid and gel, AGM yet ALL of them are subsets of lead-acid....it is just that the popular "press" presents a difference due to ignorance) follow the same general electrochemistry they ALL benefit from enhanced stable values of internal resistance, Amp-hour delivery, and (most importantly) kilo-Watt-hour repeatability when submitted to a charge regimen approaching (or even "pushing beyond") an Amp-hour-law profile (one which is approached by the so-called three-step method..actually not too bad). As a note here I need to mention that some "pulse-charging" regimens have failed to produce the results that an ordinary three-step charging regimen produces...there have been no published comparisons between the two methods, merely comparisons to simple single-point voltage regulated methods which have been proven to be (even from the textbooks) inadequate for recovering deep-discharge lead-acid batteries. Guess what? There is no comparison with the traditional known successful methods of keeping starting batteries charged using fixed charge voltages with the methods of recovering deeply-discharged batteries designed for such use.

Keep in mind that what I have written about the "Amp-hour-charging" method is not my idea it is merely my promulgation of what has appeared in the literature from a time before I was born yet has not been promulgated as a viable method due to the missing (up until this time) technology which facilitates such charging. Such charging REQUIRES a "real" battery monitor capable of measuring/monitoring real-time the kilo-Watt-hour (yeah, and the rudimentary Amp-hour) true energy charge and discharge cycling of a battery. Obviously it also requires a charger capable of being controlled or enhanced with such information. Now the REAL deal here is that, because of the inherent physics of all lead-acid batteries to decrease their charge-acceptance with a continuation of capacity accumulation (notice that I did not state "state of charge" which is different...think about it) it is relatively easy to use a 3-step "settable" charge regulator to more approximate an Amp-hour-law charge regimen with a few manual changeable settings, the first, and most important, the upper limit of the so-called "second-step" which is the acceptance limit. Setting that value higher than 14.4 V, for example, to 14.7 or 14.9 V will, for many battery types, allow an Amp-hour-law charge regimen to occur.

Here one MUST have a "real" battery monitor that is capable of displaying the number of "missing" Amp-hours from the battery so that one can at least manually set the charge voltage lower should the charge current vastly exceed the number of missing Amp-hours from the battery..one can visualize that this is a continuing decrease in charge Amps yet it is the natural decrease in charge acceptance which will allow you, the user, to only have to vary the charge voltage limit twice during the entire charge cycle to justifiably follow the Amp-hour-law...Try it and you will see for yourself if you have a "real" battery monitor to show you what is dynamically going on.

O.K. too much information!

What follows with questions?
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Old 02-11-2006, 07:33   #8
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So Rick, when will that new charging computer regulator gizmo be available for $39.95 in WalMart? Surely, between cheaper chips and offshore electronics, SOMEone can bring it in under $50?
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Old 02-11-2006, 08:01   #9
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Rick:

What do you recommend as a "real" battery monitor? is such a thing commercially available?
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Old 02-11-2006, 09:23   #10
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"Real" battery monitors

The Link series (Link 10, 1000,2000), and the E-Meter (link 10) are "real" battery monitors in that they measure true energy (Watt-hours) into and out of the battery with sufficient precision.

There may be others. I do not know if the latest Xantrex monitor utilizes the set of algorithms (which they bought in terms of the patent rights, etc. from the Link series) which, in my opinion, are at least a minimum for proper battery monitoring of AGM and gel-cell batteries.

As far as I know there is no regulator/monitor which implements the Amp-hour law charging algorithm nor do I know if anyone is even working on such a product. The last time I had a meeting with Xantrex engineers (many of whom are no longer working there) they had a full plate of badgering managers urging different types of product development.

Because there is not a huge market for a monitor/charger/Amp-hour-law regulation scheme I doubt that such a product will be inexpensive.
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Old 02-11-2006, 10:37   #11
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Hi Rick,
how do you measure the inner resistance of a batterie. as i understand, this is a very complex value an I would like to know how to get to it.
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Old 02-11-2006, 14:39   #12
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battery internal resistance

The basic idea is to measure "delta-Volts" and "delta-Amps", ideally at the same time, for a heavy incremental load that is either being added or removed from the battery. The resistance is delta-V divided by delta-I (I for Amps). One convenient method is to use either a 800 Watt to 1500 Watt heater on a power inverter or use a microwave oven while taking the readings.

Do not begin with a battery that has just been removed from a charger at full charge unless you take the time to apply the load and watch the voltage drop until it is stable at a slow linear drop in voltage versus time. Initially the voltage will drop as the curve of Epsilon and settle into a more linear rate of change or actually stay at one value for quite awhile until a more significant decrease in capacity occurs. One benefit for making this test with a heavy load that you will actually use while hanging on the hook is to determine if your battery bank size is sufficiently large so as to drive the load long enough without a significant drop in voltage over time. This is a good benchmark test.

Record the voltage and current data for both the application of the load as well as the removal. Note that after removal of the load the voltage jumps up and then gradually increases (again, as the curve of epsilon) due to the recovery of the battery from the load (electrolyte in the vicinity of the plates becomes richer in sulpheric acid and lower in water content as the electrolyte becomes more uniform). You may record several cycles and average the results.

Keep in mind that the resistance increases (not linearly) as the state of charge decreases. A reasonable guideline is to make your battery bank size to have an internal resistance sufficiently low so that the heaviest load does not cause the terminal voltage to drop lower than 11.8 or 12.0 Volts with the heaviest inverter loads when the battery is relatively "full". Another guideline is to make sure that if you use an inverter (1200 Watts for cooking potatoes or corn-on-the-cob in 8-12 minutes on high) that the terminal voltage of the battery does not fall below 11.5 V at the end of the 8 to 12 minutes. If it does then your battery bank size or quality is too small or inadequate, in my opinion.

You can readily see that the battery internal resistance plus total connector and cable resistance all the way to the inverter input teminals should not exceed 6 milli-Ohms for decent inverter performance. Less is naturally better. Because gel-cell and AGM batteries both exhibit lower cell resistance than does any flooded-cell battery, case size for case size, that they make better minimum size battery banks for power inverters.
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Old 02-11-2006, 17:53   #13
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I'm still on the fence with my choice of batteries. I would like the AGM's for the ability to be almost gasless when charging and no worry for spilling. Then there's the excellent reputation of the Trojan T-105's. I plan to install the house battery cabled directly to my starting battery with the use of a Blue Sea 9012 solenoid for isolation. Is there going to be a problem with this scenario, an AGM being charged with an automobile alternator? I'm not sure about the charging characteristics associated with car battery regulators whether or not they have a three stage charging system similar to inverter/chargers. They must have something or car batteries would be boiling over.
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Old 02-11-2006, 18:42   #14
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skyking2,

You said, ".... I plan to install the house battery cabled directly to my starting battery with the use of a Blue Sea 9012 solenoid for isolation. Is there going to be a problem with this scenario, an AGM being charged with an automobile alternator? ...."

Would need more info about your setup to respond fully, but from what you've provided it would seem you need to go back to the drawing board, because:

1. A Blue Sea 9012 solenoid will not "isolate" the banks; it's just a remote switch -- an expensive one at that -- and you would not normally want to connect the starting battery to the house battery bank.

2. An automobile alternator/regulator is not a good choice for charging house batteries. It does not have the "smart charging" capability of a real smart-charge regulator, and will not give you a full charge unless you're a motorboat, running the engine a lot. You need a smart regulator and, depending on the size of your house battery bank, an alternator capable of putting out sufficient amperage at high temperatures to efficiently charge your battery bank.

A good way to set this up these days is to use a small device like an Echo Charger from Xantrex (others make them, too) to keep the starting battery charged. You hook up the output from your alternator/regulator (and from all other onboard charging systems) to the HOUSE BATTERY BANK only. The EchoCharge device then provides charging up to about 15A as needed by the starting battery whenever it senses a charge voltage on the house batteries. Starting batteries don't need much charging capacity to keep them topped up, because very little energy is used in engine cranking (lots of amps, but for only seconds).

Bill
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Old 03-11-2006, 14:18   #15
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Thanks for your reply Bill. Sorry, I should have been more specific. Using a heavy duty solenoid is common in trucks that use winches and rv'ers. You get a solenoid rated for heavy amperage and continuous duty. Not the ones rated intermittent duty for starting an engine, although they can look the same. Run heavy cables from the starting battery to your house battery with the solenoid on the red lead. The small coil wires will be connected to a switched 12v source and ground. When the engine is running the solenoid connects the batteries to each other and they both get charged. When the ignition is off the solenoid drops and the batteries are then isolated. The diode based battery isolators apparently have a one volt loss so the solenoid is a popular way to go. What I was concerned about was if and alternator charging an AGM and the wet starting battery would cause any problems. I see that Optima makes car starting batteries so maybe there isn't a problem. As far as the 9012 being expensive, I found someone in Canada auctioning a new one and I got it for $52usd plus shipping. I'm also going to install a Prosine 2.0 which does have a three stage charger and would plug in when possible but the alternator would be used to keep a charge while going down the road or for when there isn't any shore power. I might even buy a small generator, if I have the space, to plug the inverter into for charging. This setup is for a future camping van I'm building next spring. A different hobby I know but similar situations with power requirements.
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