I dont know what could be the problem, BUT last thursday I saw some black smoke coming from the bottom of my engine (I STILL dont know what that is), but since I was hardly using the car (only moving it from side to side on the street due to alternate side parking) I haven't taken it to the mechanic yet. However the car wont start unless it gets boosted, and something has to be draining my battery because if I leave teh car idling (and on) the battery volt meter goes idles at 12V (when it should usually be 14), if I drive around a lilttle it will recharge to maybe 13V, if I take it on the highway it'll give me the complete 14V charge that it should be at. However I don't know what is draining the battery, yesterday I drove the car on the highway, after I parked it it would turn on, I left it there for like 5-6hrs and while hte battery still had charge (remote worked, etc.) it wouldn't turn on w/out a boost, when I tried to turn it on the lights (ABS/BRAKE, etc) would just flash and the starter wouldn't even kick in. Btw, I changed my ignition switch about a month ago (that shouldn't be it though?) I also replaced my battery recently, so the battery isnt the problem because its no more than 3 months old. But the battery that was in there before wasn't powerful enough for the car (it was what the auction house had in there when I bought the car).

Ideas?

bring the car to a shop and have the mechanic put a load tester on it. That will determine if it is the battery or alternator.. Ant good mechanic shop will have one.

Hey:

My car did the same thing.(2002 A6 - 2.7T). It's the altenator most likely. When mine went, I took out the FM radio also. Best bet, change the altenator and the battery. Mine has been great since.

Also have them check for a parasitic draw. The fact that your voltage goes up when you drive the car indicates the alternator is charging. Something may be draining the battery after the car is shut off.