Would an alternator run down a battery?

An alternator is designed to charge a car's battery while the engine is running, not to run it down. However, if the alternator is malfunctioning or not functioning at all, it can lead to the battery becoming depleted, especially if electrical loads exceed the battery's output. Additionally, if there are excessive electrical draws from accessories while the engine is off, the battery can be drained regardless of the alternator's state. In normal operation, though, an alternator should keep the battery charged.