'Equalizing' is not a charge procedure recommended for AGM batteries.
Lifeline AGM batteries, which are intended as Deep cycle AGM batteries and are likely unheard of in most of the automotive world, and in my opinion make the best Deep cycle AGM batteries, have both a 'reconditioning' procedure as well as a 'recovery' procedure, and both of the charging parameters are well above and outside the maximums listed by other AGM battery manufacturers.
http://www.lifelinebatteries.com/manual.pdf
Lifelines 'conditioning' procedure is similar to a flooded battery's equalizing procedure. Their deep discharge recovery procedure recommends extreme voltages.
Both will cause the vents to open and release some gas. people tend to think this is instant death for an AGM. It is not.
If an AGM is used as a starting battery only, and on a modern vehicle which does not sit unused for weeks on end, One can pretty much just leave it to the vehicles charging system to care for it.
If one cycles their AGM below 95% state of charge regularly, then the vehicles ability to hold absorption voltage as long as required, really comes into play in battery longevity.
A modern vehicle sitting for 3 weeks undriven/unstarted/idled constitutes a deeply cycled battery, and such a battery's charge requirements, if an AGM, are different than a flooded battery. The AGM depleted to 50% can easily suck everything an alternator can make, and do so for longer than a flooded battery.
While AGMs can accept huge currents when depleted and can recharge faster than their flooded counterparts( if extra charging current is available), getting that last 20% takes a long time no matter the charging source. That last 5% can take as long as 80% to 95%, and 50 to 80% can take half the time of either if the initial amps are available.
The trick to fully charging an AGM, or even making an estimate as to state of charge, is done by applying a charging source which shoots for the manufacturer recommended absorption voltage, and having an Ammeter to see how much current it accepts when absorption voltage is reached at the battery terminals.
Lifeline dictates 0.5amps per 100AH of battery capacity at 14.4volts at 77f.
Battery voltage means very little unless fully charged rested open circuit voltage is determined beforehand, and AGMS can really hold their surface charge for a long long time, especially in cold weather.
So the proclamation 'I saw 12.8 volts so my battery is fully charged'
Is inaccurate in the extreme, especially on an AGM.
So top charging an AGM is wise. They are really less tolerant of partial state of charge cycling, compared to flooded deep cycle batteries.
To top charge, apply a grid powered charging source capable of applying the manufacturer recommended absorption voltage until amps required to hold that voltage taper to 0.5% of capacity.
It is not easy to get an automatic charging source to seek absorption voltage when the battery has been alternator recharged recently. One might need to trick the charger by reducing battery voltage by the lighting and restarting the charger.
I use a 40 amp adjustable voltage power supply as a battery charger. I have a wattmeter on the output, and a separate shunted battery monitor, which has been a wonderful learning tool.
My Northstar AGM loves a high amp recharge from the most depleted state.
So with an AGM, goose the voltage upto 14.4v or so. Do amps quickly taper to 0.5% of capacity? If so then the battery was fully charged or very close to it.
If amps only taper to 2% of capacity in a few minutes, then it might take another hour or even 2 hours held at absorption voltage until it tapers to 0.5%.
Since AGM batteries are 2 to 3x as expensive as their flooded counterparts, it makes sense to make sure they can indeed get to a true 100% State of charge as often as possible, and very few grid powered charging sources, can do this automatically, especially since AGM manufacturer recommendations as to ideal charging parameters, vary so widely.
A blinking green light means nothing.
Amps flowing at absorption voltage mean everything.
I've seen my AGM take 10 hours for amps to taper from 2 amps to 0.4 amps at 14.4v, and I've seen it take only 45 minutes.
Most automatic chargers hold absorption voltage via a time based algorithm, not via amperage.
I'd love to be able to put my power supply and my amp gauge on an AGM battery fresh off the automatic charging source that is the topic of this thread. I bet most batteries would need absorption voltage held for another hour or 2 or 4 before amps taper to 0.5% of capacity
