I am not a car guy. I own a 97 A4 1.8L. Bought it a year ago. Haven't had any big issues. Tend to leave my lights on every month or two and the battery dies. Here's my issue:

two weeks ago I left my lights on and needed a jump to start it. It ran fine to my house. The next morning it wouldn't start so I jumped it again and let it run for a while. It ran for 3 days before it died on my way home. Then a jump would start it, but as soon as I unhooked, it died. I charged it overnight and it started but ran very rough (400-600 rpms at idle, normal is 900-1000) and died on my way home two starts later. I took it to a friend who checked the Alternator (working fine) and battery (working fine). He ended up cleaning out my throttle body. When I got it home, it was back to not starting. I charged it overnight again and it ran rough again and only lasted a day. A few days later I charged it for only a couple of hours. It ran perfectly for two days until, during on of the drives, I turned on the AC. The battery gauge started to dip and as soon as I rolled down my window, the battery light came on and it died in my driveway.

Seems like something isn't broken, just tweaked since leaving my lights on started this whole mess. It's as if the car can't give the battery any juice on its own. I'm hesitant to hand it over to a mechanic since it will likely cost a fortune and be a costly guessing game until the solution is found. We don't have an Audi dealership where I live.

I really appreciate any help

 

voltage regulator

 

thanks.

My buddy tested the alternator and said that the voltage was testing fine. Could it still be the voltage regulator? Again, I am not a car guy.

 

I bet its the battery. Not sure how he tested it but if he only measured voltage its not really a viable test. Acid weight is better way to determine if a battery is okay or not.

 

He's actually the parts manager at a Honda dealership. He did the work himself to avoid handing it over to a tech and racking up a bill since they are not real familiar with Audi's there and they would be starting from scratch trying to diagnose. His battery test was legit. He said it actually came back at about 98%. The battery is only about 2 years old.