The job of the battery is to start the vehicle. Once the vehicle is running the alternator is what keeps all of the electrical components running.
If the vehicle is stalling out at lights there is something else wrong. If you had trouble starting it again because there was no power, this might indicate a battery problem.
I would suggest that you take it to a certified shop or dealership to have your problem diagnosed, as there could be different reasons that this is happening. Good luck.
〉 Answered on Aug 11th, 2007 by Lori Johnson, Owner and Instructor at Ladies Start Your Engines