The electrical connectors and the internal moving parts in the voltage regulator can wear out over time, leading to regulator failure. If the voltage regulator fails, it can result in an output that is too low to charge the battery (undercharging) or too high to safely run the electrical system (overcharging).
Low voltage may result in your electrical components running poorly. Your headlights or dashboard lights may dim, especially while you are idling. Low voltage will also lead to the battery undercharging because once the alternator is outputting lower voltage than the battery (or not at all), the vehicle will be drawing off the battery instead of the alternator. With a drained battery, you may find that it is hard to start your car or that it won’t charge at all. Even if the car or truck is jumpstarted from another one, it will die once the other vehicle is disconnected, which is not the case with just a dead battery. The starter, of course, relies on power from the battery. Consistent undercharging can shorten the lifespan of the battery. The charging process keeps oxidative products from developing on the battery plates. Undercharging lets this “crust” build up, which makes it harder for the battery to take a charge going forward.
High voltage can damage electronic components and potentially the battery. Most components can handle up to 16 volts before getting damaged. Above that, and you can have some big issues as any number of electrical modules could burn out as a result, including the engine computer or body control module. If your headlight or dashboard light bulbs receive too much voltage they may burn out as well. If you find yourself replacing light bulbs frequently or unexpectedly, there may be a problem with the voltage regulator. High voltage can also lead to battery overcharging, which is highly dangerous. Battery overcharging can lead to corrosive materials escaping the battery, and potentially even to the battery exploding. A battery that gives off a sulfur smell or makes noise is a sure sign of overcharging and should be avoided.
