Dead battery => ANGRY WIFE

[Joe Garibaldi <joegari@cdc.hp.com>]

Hello all,

The wife is ready to take my head off because her daily driver (87 5KS)
has left her stranded twice in the past week.  MY responsibility, you
see, is to ensure that these kind of things don't happen (to her car
but especially to HER while she's driving it).  In order to maintain
domestic tranquility (as well as ensuring my own safety), I beseech you
to help me troubleshoot this problem.

As a prelude to my problem, let me tell you that we've been having a bit
of a heat wave here in the SF Bay Area the past week, so the A/C has been
getting quite a work-out. (Clue #1)

After the second occurence of the battery voltage going south, I took the
car out for some data gathering.  While driving ON THE FREEWAY and under
minimal load (i.e. no lights, no A/C, not even the radio), I monitored
the system voltage using Channel 11 and found it to be ~ 14.3 Volts. (Clue #2)
After turning on the lights the voltage didn't change much, only a few tenths
of a volt. (Clue #3) Next, I turned on the A/C with the blower motor set to
"low".  The voltage dropped to ~ 12.9 V. (Clue #4) Setting the blower motor
to "high" caused the reading to drop further to 12.3 V. (Clue #5) At even
lower RPMs, while driving in the city or at idle, the voltage was going as
low as  ~11.8 V.  (Clue #6) No wonder the battery was discharging!  

What component of the electrical system do you suspect as being the likely
culprit?  Battery?  Alternator?  Voltage Regulator?  What sayeth the 
communal wisdom of the great and mighty Audi listers?  HELP!  My wife's
about reached her limit.  No procrastination with this one.  If it's not
fixed by this weekend she's threatened me that it's going into the shop.
Wouldn't a mechanic have a field day with this one?

Anyway, TIA for your assistance.

Joe Garibaldi                                 e-mail: joegari@cdc.hp.com