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Old 11-01-2014, 07:25 PM   #1
Art161
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Default Overcharging AGM batteries while driving

I was reading a technical book about electronics, and am interested in what it has to say about absorbent glass mat (AGM) batteries. While the book says that AGM batteries are an improved lead acid battery, there was one item that concerns me.

The book says that while AGM batteries can be charged to 2.40 volts per cell without problems, the float charge should be reduced to 2.25 to 2.30 volts per cell and perhaps less in the summer. It further states that automotive charging systems designed for flooded lead acid batteries often have a fixed float voltage setting of 14.40 volts (2.40 volts per cell), and that this could result in overcharge on a long drive.

Does anyone here have comments or an experience with overcharging?
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Old 11-03-2014, 12:49 PM   #2
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I searched and found a similar article. From what I can tell AGM and what I take away from it, is not ideal for DD cars. Gel Cell is still the best.

http://batteryuniversity.com/learn/a..._glass_mat_agm

"AGM and other sealed batteries do not like heat and should be installed away from the engine compartment. Manufacturers recommend halting charge if the battery core reaches 49°C (120°F). "

That means trunk mount and even then, on a hot summer day a trunk in temperate climate could easily surpass that, in AZ, ambient temps could run that hot.

" Automotive charging systems for flooded lead acid often have a fixed float voltage setting of 14.40V (2.40V/cell), and a direct replacement with a sealed unit could spell trouble by exposing the battery to undue overcharge on a long drive."

http://batteryuniversity.com/learn/a...d_acid_battery

Again, not worth it. Go with a gel cell battery if you want better performance for your car unless it's a special application that is designed to handle an AGM battery.
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Old 11-03-2014, 06:55 PM   #3
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The book I am using is the 2015 ARRL Handbook, and it doesn't have much to say about gel cells. It does state that "Heat can be a problem for AGM and other gelled electrolyte batteries." I'm not prepared to discuss the advantages and disadvantages of gel cells, because I don't know much about them.
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Old 11-04-2014, 09:05 AM   #4
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We use AGM batteries in various UPS applcations and, as far as heat goes, they have a rather narrow band of preferred operating temperature and can experience "thermal runaway" faster than other battery types. I havent researched it enough to be able to say that it would prevent or limit their use in an automotive application.
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Old 11-04-2014, 09:05 AM
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