Another Electrical Puzzle

Here's one for the experts...

2001 Audi A6, 50000 miles.

This has been a fairly trouble free car except for front end woes fixed
under warranty and one electrical gremlin that occasionally blows fuses
to the rear power outlet (lighter).

Anyway, my wife drove it all day in the rain today, starting and
stopping at various places with no apparent troubles. Tonight, she
stopped for 20 minutes, and when she came back to it to start it, all
she got was clicking. She tells me the interior lights were fairly dim.
OK...so after she panicked a bit on the phone, she called back and said
that the interior lights got bright and the car started. The only
remaining symptom was that the radio is in "safe mode" as though the
battery had been disconnected.

So....it sounds like a dying battery that couldn't turn over the
starter....except why would there be low juice at first and then enough
to start it 10 minutes later? It wouldn't be a loose connection, because
there should have been no power at all. I'd suspect the alternator, but
then the battery should have just died and stayed dead. Could it be the
starter itself -- can the starter gears "jam"? (for lack of a better
term) Moisture somewhere? Or just the usual 2001 A6 electrical gremlins?

You can certainly see that figuring this out could run into serious
money as the mechanic spends hours and hours looking for something that
is no longer there -- until the next time, that is.

Maybe time for new battery, at least?

--
Wayne Crannell
Xxxxxxx, TX