I left a mirror light on overnight without noticing. it discharged the battery to the point of almost not starting in the morning. but it did start and run just fine. I had to re set the clock though. drove it 13 miles to work, parked it and still had not noticed the mirror light. it sat all day with the light still on and discharged the battery until it once again almost would not start the car. but again the car started and ran ok. but now, the clock had to be reset again and the ac was blowing hot air and would not respond to changing to a cold setting--still blew hot air. I shut off the car, checked the battery--still shows green eye, no loose or corroded connections at battery in trunk or under hood. checked fluids while under hood and they were fine. went to re start engine and it would not start==battery too discharged to crank over the engine. that is when I noticed the mirror light and turned it off. I called a tow truck and the driver jump started the car. It started up but then the engine started surging instead of idleing smoothly. When I stepped on the accellerator, there was no response. I shut the car off. tried it again, same results. I had the car towed home. It has sat in the driveway for a couple of days. at first, it would not crank over. but the battery has recovered some from sitting and I started the car tonight. but it still surges while idling and won't accellerate. The tow truck driver told me I may have to have it towed to the dealer to "have it re-set" He said whenever the battery is disconnected on a bmw around that year, 2004, z4, it has to have something re-set by the dealership. Is this true or do I have some sort of damage caused by the way the car was jump started? I saw that the positive cable connection was made correctly to the terminal in the black plastic box on the fire wall, but I did not see where the ground cable was connected. I assumed he did it correctly because the car started. But what caused the ac to pump hot air, clock need re setting, and then the engine surge...?