Audi gods tease

["Michael Benno" <mbenno@northstar-mn.com>]

This is really weird:

This morning it was -8 degrees, Audi started. After scrapping the frost for
a few minutes the car was running really rough. I gave some gas (tank full)
but the revs didn't rev. I turned off the car and tried to restart. Nothing
but relays clicking and the good old battery warning light was on. Volts
read 8. 

This was very odd, I have never had a problem starting my car. It started
last year at -37 degrees F, no problem (well a little stiff). The battery
is 2 years old.

I bought a charger (grr) and charged it and started the car. Everthing is
okay? Volts are charging at 14-15 so the altenator is working fine, right? 
No warning lights. What is up? Do I replace the battery?

Michael Benno 90q 20v