I had that same problem w/ my 02. It was the alternator. They said it was the battery. I told them I replaced it w/ a new one. We drove the car and it totaly shut down on me. I had it towed to the dealer and told them that I thought it might be the alternator. They told me Porsche alt's DO NOT go bad. Well, low and behold I was right

. They had to replace it. NOT CHEAP! But luckily mine was covered. After all was said and done the bill was $1189!