came back from the dealer today. it was the alternator. somehow it just decide to stop functioning. but i didn't get it replaced at fairfax since my third party warranty only covers power train. guess how much they ask for, 12 bills. i said nah, thats all right. i have a shop could do it for not even half of that. they charged up the battery and let me take the car. they are good in term of service but not on pricing. anyway, i will take it to my bmw guy in alexandria. well the thing is there is no sign of failing alternator. that the dangerous thing.