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Old 28-10-2006, 14:55   #1
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Join Date: Jan 2005
Location: Seattle area (Bremerton)
Boat: C&C Landfall 39 center cockpit "Anahita"
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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.

Rick is offline   Reply With Quote
Old 28-10-2006, 15:09   #2
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Join Date: Apr 2006
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Happiness is a warm AGM, mama (apologies to The Beattles).
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