Like Sally Field..... yr. Optima  "really likes you"? (sorry, not Friday
yet)

Battery specs. are a bit like voodoo. What in theory ought to work, doesn't.
Conversely what ought not work does.

The glass mat gel in the Optima has been experienced by many  users to be
exceedingly tough and reliable.  My best guess as to your repeated draw-down
or cycling  to roughly 50% capacity each day has not significantly reduced
the batteries ability to take another charge. I believe this is called
sulfating in a wet cell batt; where repeated deep discharges below 50%
capacity, literally clog the anode/cathode  (can never recall which is
which) ) plates in the battery.  In a word, Optima's resist sulfating.

Regarding your observed lower than optimal charge voltage to your
Optima's...... huuuummmm!
As I have read Optima's web site, their Batteries like higher than the
average voltage and lots of current flow during a charge. Something the
stock VW charging system does not supply in anything that could be seen as:
in excess! You get plenty of Amps in a working Alternator but it is Voltage
limited, as you have observed.

A simplistic explanation might sound like this: The optima is one tough
(read expensive) battery. They (Optima) rate their Batteries conservatively
meaning Optima states 200cycles on AVERAGE. On a good day one might get
300-400-500 cycles. Optima's tolerate wide variations in voltage and current
during a charge.

Regards
Phil.Zimmerman@mail.crcn.net