What does the alternator warning light indicate when it is lit?

The alternator warning light indicates that there is an issue with the vehicle's electrical system, particularly the alternator, which is responsible for charging the battery and powering the electrical components while the engine is running. When this light is lit, it typically suggests that the alternator is not functioning properly and may be unable to supply sufficient power to the battery, leading to potential battery failure. This warning serves as an alert that you should check the electrical system, as a failing alternator can quickly drain the battery, leaving the vehicle unable to start or operate correctly. Hence, the identification of needing a new battery is valid, as a malfunctioning alternator can lead to a battery that is not being charged, thus requiring replacement.