If the alternator fails, approximately how long will your battery last?

When the alternator fails, your vehicle relies solely on the battery for electrical power. The lifespan of the battery during this time depends on various factors, including the battery's charge state, the power demand from electrical components, and the age and health of the battery itself.

Typically, a fully charged battery can sustain a vehicle's basic electrical needs—such as lights, ignition, and fuel injection—for approximately 30 minutes under normal circumstances. This time can vary depending on how many electrical devices are in use and the condition of the battery. If you are using more electrical accessories like headlights, radio, or air conditioning, the battery may drain more quickly than this estimate.

This is why option B is considered the most accurate, as it reflects a realistic timeframe for the battery's function in case of alternator failure, striking a balance between average usage and battery capacity.