Quote:
Originally Posted by jp.vegas
It's not a 4th or 5th get issue, it's an all cars issue. The voltage needed to fully charge an AGM battery is higher than that needed to charge a lead acid battery. Since the voltage isn't high enough, the AGM never gets completely charged and that's what causes premature death.
There are a variety of solutions to the low voltage problem.
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It is a misconception that AGM batteries need a higher voltage to charge. From the Battery University: "AGM is making inroads into the start-stop function of cars. ... As with all gelled and sealed units, AGM batteries are sensitive to overcharging. A charge to 2.40V/cell (and higher) is fine; however, the float charge should be reduced to between 2.25 and 2.30V/cell (summer temperatures may require lower voltages)."
Thus 2.4 volts/cell is 14.4 volts for the normal 6 cell car battery, which is what the nominal car alternator puts out. Those that put voltage boosters on their alternator are thus overcharging an AGM battery which is what leads to their early failure.
Also, note that the maximum float charge should be less than 2.3 volts/cell (13.8 volts for 6 cell car battery) is below the nominal alternator voltage. Thus, after an AGM battery is fully charged, the alternator voltage will be overcharging the AGM battery.
