Most def the alternator. Get it replaced with the correct one because there are two for that particular model and year. If you have a totally electronic interior you need the higher end alternator. It's actually stamped on the blade of one of the fans.
I had the same thing happen to mee on the highway during rush hour. The bad news was, the battery totally drained and the entire engine, transmission, power and steering died and I had to muscle it off to the side of the road...