Overall, a weak battery loses its charge faster and is less successful at holding a charge. This puts an additional strain on your alternator, reducing its lifespan. However, just because your battery has died does not mean your alternator will die too.
Does a Bad Battery Affect Your Starter or Alternator? A bad battery won't usually harm your starter or alternator, however, since both of those components get their voltage directly from the battery, if the battery is underperforming, both the alternator's and starter's performance will be affected as well.
This can also be due to bad diodes but can also be from a failed voltage regulator, worn brushes, or corroded connections inside the alternator, not to mention bad connections or broken wires externally.
A corroded or defective alternator diode will faultily continue charging the circuit even when the car off. This, in turn, will drain your car battery and cause the car not to start.
Can you jumpstart a car with a bad alternator? It is possible in some cases to jumpstart a vehicle that has a faulty alternator, as long as the battery has enough of a charge to keep running. However, the alternator should be replaced as soon as possible.
Alternators have a number of moving parts, so as they get dirty and are subjected to extreme temperatures, those internal components can wear out, causing the alternator to go bad. One of the most common problems you're likely to experience with an alternator is a failure in the bearings.
Alternators don't blow without any reason. Make sure to have a trained professional inspect your vehicle for any underlying issues once this happens. A blown alternator fuse can cause your vehicle to exhibit several symptoms, such as a dead battery, dim lights, illuminated warning lights, and other electrical oddities.
Parasitic Drain - If the electrical devices in your car or the lights on your car are left running even when your ignition is off, they will suck the juice out of your battery slowly but dramatically. This is often eerily described as parasitic drain.
If you can turn the engine on, but it dies shortly thereafter, your car alternator likely isn't able to charge the battery. On the other hand, if you jumpstart the car and later on it fails to start on its own, it's likely a dead battery.
However, the alternator requires some power for the car's other electrical functions, so only 50 amps are available for charging the battery. Theoretically, it would take 90 minutes to fill the battery from empty. Topping up 20% would require one-fifth of that time, or about 17 minutes.
If your alternator fails when you're far from home, you can typically drive up to 200 miles on battery power alone. That's assuming your battery is in good shape and fully charged. Of course, it's best to get the alternator repaired or replaced as soon as you can.
A bad alternator may not charge your battery, leaving it with less power. Even worse, a bad alternator can even drain your battery, even when the car is not running. If you're dealing with a bad alternator, it's probably time to head to a mechanic.
Charging problems can be caused by electrical faults in the alternator or voltage regulator, poor wiring connections at the battery or alternator, or a slipping or broken drive belt. Since most late-model import alternators are internally regulated, a failure of the regulator means the alternator must also be replaced.
That said, an alternator can take time to fail or can stop working suddenly. Usually, people recognize the whining sound that comes from a bad alternator and get it fixed before it breaks down completely.
Your car's alternator may fail for various reasons: Age and use-related wear is often the reason behind a dying alternator. Engine oil or power steering fluid leaking onto the car alternator can lead to its failure. Prolonged idling while using multiple electrical accessories can prematurely wear the alternator.
Most alternators will last between 80,000 and 150,000 miles — or about seven years. However, your driving habits and the area where you live could wear it out prematurely.
The standard symptom your alternator is going bad is the warning light on your dashboard. Other symptoms include the lights on your car are flickering or you have issues starting your car. If you hear sounds coming from the engine, it's almost definitely coming from a failing alternator.
Alternators can average anywhere from $100 to $350, depending on the model. In most cases, costs will average between $350−400 for the alternator replacement if no other parts need to be changed. Add another $20 to $50 to your bill if the serpentine belt has to be replaced as well.
If you ever hear growling or whining noises coming from under the hood, you could have alternator problems, which should be checked out by a professional ASAP. This growling or whining sound happens when the belt that turns the alternator's pulley becomes misaligned or rubs against the side of the pulley.
HERE'S HOW TO DIAGNOSE A FAILING ALTERNATOR
If you have a “Check Engine" light on, connect a code reader to the diagnostic port. If you find code P0562, you very likely have a failing alternator (note that codes may vary by vehicle make/model/year). Get it checked out before it fails entirely.