Q: My car stalls at idle; the battery is good, so is it the alternator?

This sounds like a potential problem with the charging system. The primary function of the battery is to start the vehicle. Once it is running, the alternator provides all electrical power for the vehicle. However, the battery does function as a sort of back up to the alternator. If the alternator has failed, either internally or due to the voltage regulator, the electrical system will then draw power from the battery. Since the battery does not produce power once it is drained, once the energy that it does have in reserve is depleted, there is no more electrical power to run the vehicle. There may be just enough power for things like the lights and radio to come on, but not enough to power the vehicle’s electrical needs completely. I would recommend having a certified technician, such as one from YourMechanic, inspect your vehicle to diagnose the exact cause of your stalling problem.