Chefwong, Interesting.
I wonder if it was really a tech, or an 'applications engineer', which is another term for marketer.
Was your intended application including deep cycling? A shallowly discharged battery cannot accept huge currents, and does not need them anyway. If it is a battery that has all the time in the world to recharge at float voltages, then again, high amps are not needed and would be rejected by the voltage controller on the charging source if the battery were ~85% or more charged when charging began.
One cannot force a battery to charge any faster at the 85% + state of charge range safely. To do so would require too high a voltage, which causes positive plate erosion and on flooded batteries, excessive water usage, and on AGM batteries would likely cause the vents to open and water loss as well, which of course cannot be replaced.
So at 85%+SOC, low and slow is basically the only option available. It takes time to fully charge a Lead acid battery, no matter the charging source.
But if the battery is drawn to 50% state of charge, it can accept huge charging currents, and Lifeline and Odyssey both say, the more the better, where as some other AGM's say never exceed 30% of the 20 hour capacity rate.
I spoke at length with an Odyssey engineer about deep cycling their group31 (pc2150) and recharging via 200 watts of solar only. He said flat out it was not a good match, and I would not get my money's worth from the battery. That high initial recharging currents were critical to their battery longevity. That the plates were too dense and tightly packed for lower currents to penetrate and saturate them.
The Northstar list of approved chargers is longer than that of Odyssey. Northstar relabels some Ctek chargers too. Northstar and Odyssey make so many of the same claims as to performance, and their CCA and AH can be exactly the same across batteries of the same size, that I believe ( my opinion) them to be very similar in construction and design.
901M, 'well enough' is certainly open to interpretation. The deeper the discharge the more important it is to feed the high $$ AGM at a high rate.
The lower $$ AGMS say to limit amps to no more than 30 per 100AH capacity.
So we have hugely contradictory recommendations by the battery manufacturers as to what they have determined works best on their specific batteries, yet many people, and chargers, paint all AGMs with the same brush. Some even include gel batteries in that same brushstroke, and a true gel battery needs precise current control or else it is damaged permanently the first time those parameters are exceeded.
Many people call AGM's gel cells, but Absorbed Glass Matt batteries do not have a silica thickened Gelled electrolyte, as do true gel batteries.
Lower bulk charge rates on AGM's can be negated to some degree by holding absorption voltage for longer. Odyssey says once 14.7v is reached it is to be held for 4 hours. Few chargers will do this, and Odyssey has their own line of expensive chargers meant to properly care for their batteries. But strangely, their group 31 at 100AH, which requires 40 amps when deeply discharged according to their own recommendations, well they do not have a 40 amp charger for it.
In the end it comes down to how the battery is used. I happen to deeply cycle a battery practically every day, and what makes this battery happy is a hugely different requirement than a battery which is shallowly discharged and only occasionally sees a deeper discharge.
I also have the tools and interest to observe and measure and record how my battery behaves during discharge, how much voltage it can maintain for how many Amp hours are removed from it. My Northstar AGM, after 4 nights of 50% depletion and only 200 watts of solar, has the voltage tank under the same loading on the 5th night. On day 6 I will use my 40 amp power supply + whatever the solar can contribute, and that performance returns. Really, I try and avoid deeply discharging it if I know that the solar is going to be the only charging source available, but often I just say Eff it, it is just a battery and it works for me, not the other way around.
To truly know if an AGM is fully charged, one needs an ammeter and a charging source capable of the manufacturer recommended absorption voltage and holding that voltage for as long as required.
This is why I went with an adjustable voltage power supply. I can hold 14.46v at 77f until amps taper to 0.45. Sometimes that tapering takes 2.5 hours, other times that tapering lasts for 5 hours. The time required to reach that end point, is directly related to not only how deeply discharged the battery was, but how many cycles accumulated where it was recharged ONLY by a low and slow 200 watts of solar. At this time of year this is the 11 to 12.5 amp range at solar Noon. 11 to 12.5 amps is not even considered low and slow by most.
Also, the correct float voltage can be determined by an adjustable voltage power supply and an Ammeter. If it has been floating for a period of time at 13.2v, and then one gooses the voltage upto 14.4v and the single large battery takes more than a few amps to reach 14.4, and these amps do not quickly taper back down to the 0.5% of the total AH capacity(@20 hour rate), the float voltage was too low or the battery was not fully charged when float voltages were initiated, or some combination of both
Recommended float voltages vary greatly among AGM manufacturers too. Lifeline recommends 13.2 to 13.4v. Odyssey and Northstar at 13.6v.
I found 13.4v is too low on My Northstar AGM, and the sweetspot is 13.5 to 13.6v, to maintain 100% state of charge in a mild climate.
My flooded battery was happy with 13.15v.
AGM's are great batteries. Some people think their significantly higher price somehow imparts them with magical abilities to resist abuse. But if anything, AGMS are more temperamental when it comes to how they are recharged. They require true 100% charges as often as possible, as soon as possible, and do not handle partial state of charge cycling as well as their flooded deep cycle counterparts.
Treat an AGM right and it will return the favor, but being ignorant to their requirements and having them fail prematurely, is like buying a high $$ German car, and never changing the oil, then complaining when the engine seizes saying such an expensive car should be immune to such things.
Batteries are surpisingly tolerant of charging parameters outside the manufacturer listed ideals. But still, it is good to know what those ideals are, and try to meet them.
Another pet peeve of mine is the 12.8v =100% charged mentality.
My Northstar AGM has a fully charged resting open circuit voltage of 13.06v. 12.8 OCV is about 75% charged on this battery.
My Flooded battery fully charged rested OCV is 12.72v. 12.8v on this battery indicates only that the surface charge has not abated.
Also I can get the flooded battery to read 12.72 OCV rested, and stick the hydrometer in the cells and have them read 1.225.
Fully charged on this battery is 1.285, yet the resting voltage was 12.72, even with SG at 1.225.
Voltage means so very little with lead acid batteries, yet people act like it is not only a fuel gauge, but that it also indicates battery health.
While a battery that fails to maintain 12.65v+ after the charging source is removed is likely on its way to the recyclers, just because a battery holds 12.7+, does not mean it is 'just like new!" as so many will proclaim.
I know on this forum, most are using just starting batteries, as starting batteries. But when one starts cycling marine batteries, or the Deep Cycle batteries, often and deeply, the requirements to achieve good battery longevity are much much different.
Low and slow on a battery whose next discharge cycle starts in a few hours is insanity. Low and slow on a battery that was not deeply discharged is fine and dandy.
Low and slow on a healthy battery that has all the time in the world to reach a true 100% recharge, is fine and dandy, but an older battery, chronically undercharged, low and slow has little chance of reverting the specific gravity back up to the maximum, no matter how long low and slow is applied.
And maximum specific gravity is the goal, the hydrometer on a flooded battery is the polygraph. Knowing the baseline maximum Specific gravity is required too. Batteries for hotter climates can max out in the 1.265 range, those for Arctic climates might go as high as 1.310.
On an older battery whose max SG is unknown, then an equalization charge must be performed, the hydrometer dipped every 15 minutes and the charging stopped when SG, compensated for the rising temperature, no longer rises, or battery temperature rapidly climbs, or exceeds 120F.
Voltages upto 16V can be required to maximize specific gravity.
These voltages should only be applied on a battery which was held at 14.8v or less, for 4 hours. Allow no more than 5% of the capacity (5 amps for a 100AH battery) to bring the battery upto 16V.
5% might not get the battery upto 16v. Be sure to monitor it for temperature. If the amps start rising again, terminate EQ charge.
Lifeline AGM are pretty much top DOG in the AGM DeepCycle battery world. They have a well written tech sheet:
Some of the info is relevant only to their batteries, much of it is relevant to all lead acid batteries flooded or AGM.
http://www.lifelinebatteries.com/manual.pdf
