2008 mazda 3, charging system warning light?

[Morgan A]

so about a week ago i was driving my car to go to lunch, waiting at a light to turn left when it randomly shut off & the battery light came on. i turned the whole car off with the key, and started it up again and the light went away and the car hasnt died on me since. i looked in the owners manual and it said when that light comes on its the charging system warning light and it was a malfunction that required dealer inspection. well ever since it drives weird. whenever i accelerate the RPMS bounce up and down, and the car drives jerky. i took it into mazda, and they said they tested everything (battery, alternator, etc) and it tested fine. they flushed out something or other thinkin something was clogged, but it didnt do anything. then they changed the o2 sensor, that also did nothing. so they still have my car and are putting a new catylitic (sp) converter in it. im concerned this isnt going to help! my car is fairly new. ive only had it for a month or so. its an 08 with 30,000 miles. whats the deal!?!? does anyone know what it could be????? thanks in advance!!!