Signs of a Bad Alternator or Battery

The alternator works with the battery to power your car’s electrical system. They have a mutually dependent relationship. A bad alternator and battery can hinder the proper functioning of your car. Your car may not even come up if either the alternator or the battery is bad.

Bad Alternator vs Bad Battery: How to Tell the Difference

If your battery or alternator is bad, your car might display similar symptoms.  You can only tell the difference if it’s your battery or alternator that is failing by testing your battery and alternator with a voltmeter or multimeter. This will make it easier to ascertain if the problem is from your alternator or battery.

There are several signs of a bad alternator or battery. Although these signs are similar, there are some slight differences.

For instance, if your alternator is bad, your battery will die and your engine will stall. On the other hand, if your battery is bad, you will experience a bad smell coming from your hood and trouble starting your car.

Subsequent discussions as I proceed will clarify these differences.

Signs of a Bad Alternator vs Battery
How does the alternator work?

What is an Alternator and How Does it Work?

The alternator is a source of direct electric current to a vehicle. It distributes electricity to the vehicle and charges the battery. The alternator converts mechanical energy to electrical energy to help you charge your battery and other electrical components of the car.

The alternator serves as a source of power for your vehicle when driving or when the car is idle. A car battery that is not charging can last between 30 minutes to 2 hours of driving which makes the alternator a crucial part of your vehicle because it recharges your battery while it is in use.

The stator and rotor in the alternator rotate to generate alternating current (AC) using a set of magnets which is then converted to a direct current (DC) to be used during the charging process. A vehicle’s charging system comprises a battery, a voltage regulator, and an alternator.

Signs of a Bad Alternator vs Battery
How does the car battery work?

What is a Battery and How does it Work?

An automotive battery is also known as a car battery is a rechargeable battery that powers a vehicle. Your car battery might be seen as a small box but it is the heart of your vehicle. The type of battery used in automobiles is usually known as wet cells battery. They store chemical energy which is later transformed into electrical energy for use.

A car battery provides the required electricity needed to power all electrical components in your vehicle. This is achieved by converting chemical energy into electrical energy. Also, your battery stabilizes the voltage and keeps the electric current in check.

How to Check if your Alternator is Working

The easiest way to check if your alternator is working is by testing it with a multimeter or voltmeter.

The test helps to determine the condition of your alternator. You can begin by checking the starter solenoid which is positioned on the starter and serves as an electromagnet relay that engages the starter.

The starter solenoid is checked through a physical inspection of wires. In the course of this, if you notice the wires are not damaged and are connected properly  then you can proceed to check the voltage.

Checking the voltage requires a multimeter or voltmeter. Your alternator should read between 12.6 and 14.2 volts when being tested with a multimeter or voltmeter. If your alternator reads lower than 12.6 or higher than 14.2 then there’s possibly an issue with your alternator. If it fluctuates between 12.6 and 14, your alternator is in a good condition. A lower reading indicates that your alternator is having a voltage issue. If it reads 12.6 it is getting low but will still work properly.

Signs of a Bad Alternator or Battery
How to test your car battery

How to Check if your Battery is Working

Testing your battery from time to time helps reduce the chances of failure. You can check if your battery is working by testing it with any available battery testers or better still a voltmeter or multimeter.

Using a multimeter to check if your battery is in good condition is quite easy if you follow some basic steps.

In testing your battery, you need to do the following;

  • disconnect the battery from your car.
  • perform a quick visual inspection.
  • set up and connect the multimeter.

In setting up your multimeter, you need to adjust it to 20V of DC voltage or anything above 15V of DC.

After adjusting it, to get an accurate reading, you place the red probe of the multimeter on the positive battery terminal and the black probe on the negative terminal.

You should get a reading of 12.6 to 14.8 if your battery is in good condition. Anything below this range is a sign that your battery is drained and not in good condition. 

If your battery does not read properly during the multimeter test, it’s a clear indication that your battery is dying and will not work properly.

Signs of a Failing Alternator

Squealing, growling, or grinding noise

Growling or squealing noise emanating from your alternator is an indication that your alternator cannot turn properly and when this happens, it means that your alternator is failing.

The sounds can also come from a misaligned alternator belt coming in contact with the alternator pulley or a broken part of the alternator.

Engine stalling

When the power of your car is very low, your engine will begin to stall.

The power of your vehicle will get this low if your alternator is bad because the alternator serves as a direct source of electric current for your vehicle.

Check engine light comes on

The check engine light or dashboard warning light can come on if there is a problem with your alternator.

People usually mistake this for a battery problem, rather this could be an indicator there is an issue with your car’s electrical system which also includes the alternator. The dashboard light will be flickering on and off because the alternator is unable to supply adequate power.

Alternators are designed to work between 12.6 to 14.5 volts. If the voltage drops below this, it’s a sign that your alternator is failing and will cause your check engine light to start blinking.

Bright lights that dim quickly

Inconsistent voltage, which makes bright lights go dim suddenly is an indication that your alternator is bad. Your dashboard light and other lights in your vehicle can be extremely bright at a point and go very dim in a short time.

Your car lights are powered by the car battery and while driving, the alternator is meant to provide the needed power to keep the lights bright. If the alternator is failing, the lights will go dim.

Dead battery even when it is changed

A dead battery is another sign of a failing alternator. A bad alternator will not charge your battery properly while your car is in motion causing the battery to die down faster. A battery is designed to power your car for 30 minutes to over 2 hours, it is the duty of the alternator to continue charging your battery within this time.

If your battery dies after this time, then there is certainly a problem with your alternator.

Engine stops running once the positive terminal is disconnected

If your car goes off when you disconnect the positive terminal from your battery, it means that your alternator is bad and unable to generate the necessary power to keep the car going.

Signs of a Bad Battery

Difficulty starting the car

Difficulty in starting your car is one issue associated with a bad battery. The battery is the life of your car because your car depends on it to start. When your battery is bad, it will not deliver the level of amperage required to start your car, thereby making it very difficult to start.

Other times the fault can be from the alternator if it is bad because it will fail to charge up the battery.

Bad smell from the hood

A bad battery can emit rotten egg or sulfur odor from your hood. This odor usually emanates from a leaking battery which is a sign that your battery is damaged.

Your battery can get damaged as a result of natural wear and tear, cracks, or bloating.

Car cranks slow

Your engine cranking slowly is a sign that your battery is not fully charged or is bad. Your car will take longer to start because your starter is not getting enough electricity to power it.

This can be experienced when you turn your ignition and your car is turning over or starting slowly.

The engine gets amperage from the battery to start and if your battery is dying or bad, your engine will be slow to crank.

Damaged or corroded battery terminals

Sometimes if your car refuses to start, it might not be that your battery is dead, rather, there may be a problem with your battery terminals.

Corrosion around the battery terminals can make it difficult to start your car and eventually damage your battery. The battery terminals transmit electric power from the battery to other components of the car.

If these terminals are damaged or corroded, components of your car will not get the required electricity and it will give the impression of a dead or damaged battery.

Dim headlights or interior lights

If your battery is failing, your headlights or interior lights will be dull or dim because it is not getting the required amount of electricity needed to make it work well. Your dashboard and radio lights will become dim as well if your battery is bad. Your headlights can give you a strong indication of your battery strength if you try starting your car and it is not responding. 

If you see a dim light your battery might either be undercharged or failing.

Cost of Alternator Replacement

Once you’ve experienced the different signs of a failing alternator, it is important to get it fixed as soon as possible.

The cost of the alternator will vary based on the model and brand of your vehicle.

A new alternator costs between $200-$500. The cost of labor is around $100-$200.

Cost of Battery Replacement

At some point, you will have to replace your battery if it is bad or has been overused.

There are different types of automobile batteries available for your car. Batteries can cost around $50-$200 depending on the type and quality.

Lead-acid battery which are one of the most common for cars costs $125-$135 while absorbent glass mat (AGM) batteries cost over $200 because they are strong and durable and can power the most sophisticated electronics in some luxury vehicles.

FAQs about Battery vs Alternator

What can damage an alternator?

Damage to the alternator can be either electrical or mechanical. Mechanical damage will cause the failure of bearings or fastener while electrical damage will cause difficulties while starting the engine, weak headlights, winding rupture.

The following are factors that can damage your alternator:

  • Bad fuse.
  • Broken pulley or belt.
  • Wiring problems.
  • Computer problem.

How Long does it take for a Bad Alternator to Drain a Battery?

If your alternator is bad, your battery can last for just 30 minutes and if you’re lucky, it can go up to 2 hours. Remember, the alternator is a source of electric current to your vehicle that also charges the battery. So, if it is bad, it will not charge while your battery will keep providing energy to headlights and other components of the car. This will cause your battery to drain in about 30 minutes or more.

Can a Bad Battery Damage the Alternator?

No! A bad battery won’t damage the alternator but a bad alternator can damage your battery. The car battery isn’t designed to provide electrical power for a long time hence the need for the alternator, so if your battery is bad, your alternator will be idle and will not be damaged.

Can Jump Starting Damage Alternator?

Jump starting is the process of starting a vehicle with a depleted battery. You can jump-start your car without damaging your alternator by using the right techniques. The electrical system of modern vehicles is quite complicated and requires caution when dealing with them. You can safely jump-start your vehicle without posing any risk to your alternator by using a battery jump box.

Will a Car Start with a Bad Alternator?

Yes! you can start and drive your vehicle with a bad alternator, but this will only last for a few minutes because your battery will not get the required charging and will eventually go off after a few minutes. The bad side of this is that your car will go off without notice and leave you stranded.

Do Alternators Fail Suddenly?

Alternators can fail suddenly or over time. Your alternator can fail as a result of prolonged usage or fluid leakage. It is rare for alternators to fail suddenly, but this does not mean that it does not happen. Alternators usually exhibit several signs of failure before they eventually break down completely.

How Do I Check to See if My Alternator is Bad?

Several ways to know if an alternator is bad and tools to test them had been discussed earlier. You can also check this through a battery or headlight test. The headlight is quick and easy. All you need to do is to start your car and put on the headlights, press your accelerator and ask someone to observe your headlight. If the lights get dim, too bright, or flicker when the accelerator is pressed, it means your accelerator is bad. Whereas for the battery test, what you need to do is quite simple as well. You need to open your bonnet and start your car, as the car is still running, disconnect the negative battery terminal. If you see the vehicle stalling, there is a possibility that your alternator is bad.

How Long Does an Alternator Last?

Alternators are designed to last for a long period. They are more durable than batteries. Most alternators last around 150,000 miles which is between 7-10 years. Driving through rough conditions such as dirt, sand, snow, and rain can reduce the lifespan of your alternator.

How Long do Batteries Last?

The durability of a battery depends on the quality and type of battery you purchase. Most batteries have a shorter lifespan than alternators. Low-quality and less-expensive batteries can last between 2-4 years while high quality batteries will last for up to 5-7 years.

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