What occurs if a vehicle's alternator fails?

When a vehicle's alternator fails, the most immediate and significant consequence is that the battery cannot be charged. The alternator plays a crucial role in generating electrical power while the engine is running, and it charges the battery to ensure that all electrical systems function properly. If the alternator is not working correctly, the battery will slowly deplete its stored energy, which can eventually lead to a vehicle that won’t start or run properly when not running on the energy it has left.

While some might think that the engine would stop immediately, that's not typically the case as the vehicle will continue to run using the energy already stored in the battery for a limited period until it drains. Similarly, the vehicle may start if the battery has a sufficient charge at the onset of the alternator's failure. An alternator failure does not directly lead to decreased fuel efficiency, though the strain of running on battery power alone can eventually result in other performance issues, including inefficiencies related to insufficient electrical power to critical systems.