Fast charging just about any battery will reduce its lifespan, so it's a good idea you had, to slow charge
it (any time you can). The slow charge is not a longer lasting charge, though, assuming you charged to completion in both cases.
Using the voltage to measure the degree of discharge is not the best way to do it, but it is the only way you have of determining the state of charge (or condition) of an AGM battery.
The most reliable way to determine state of charge of a battery is to use a hydrometer and measure the specific gravity in each cell.
Unfortunately, this cannot be done with an AGM battery because the electrolyte is not free (it's absorbed into the glass mat), and the cells are sealed and not accessible.
A brand new battery like yours will improve initially in its performance for the first few dozen cycles or so, then, like all batteries, it begins to gradually lower in performance over the remainder of its service life. If your voltmeter is sensitive enough to resolve this, and you monitor it closely, you might be able to see this in your voltage readings. But be sure to let the battery sit for several hours after charging before taking your reading to insure you are not reading a short-term residual charge.
Regards- Brian
and it has been fully discharged a couple of times but not for long, be careful with some of the agm and calcium batteries as if they get down too low they won't charge without a high voltage charger to recondition them.
