As per How do you know if the replacement battery is a good one?, it may be the case that I've purchased a battery that may not be at its best.
I got it from a VW dealer installed on 2016-10-01; it had the coloured dot of "9/16", but also an inscription of 3216 near its negative terminal, which, if read as 2016-W32, would correspond to the week of 2016-08-08/14.
I've noticed that these coloured dots are often one month ahead of the current month, e.g., in mid-August 2016, I vaguely recall already seeing a couple of "9/16" dots at a Walmart.
Various sources may indicate that the lead-acid batteries may self-discharge between as low as "5% per month" (per BatteryUniversity) to as high as "approximately 4% a week" (per ProgressiveDyn). And here in Texas with 100°F / 38°C heat being all too common in the summer, it might indeed have self-discharged the full 25% during the nearly two months that it sat idle.
I've placed some fancy Stanley 15A charger onto it; it's been two hours, and it currently shows that it's still charging at a rate of 4.4A and is still only 75% charged (their indicator logic is defective?), and still hasn't reached the "float" mode.
Should I return this expired battery, and ask for one that's not been expired yet?