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Signs Of A Bad Car Battery Vs. Alternator – What You Need To Know!  

Signs Of A Bad Car Battery Vs. Alternator

To determine the main signs of a bad car battery vs. alternator, you need to know what an alternator is, the battery’s function, and the signs and symptoms of faulty alternators and batteries. Knowing these symptoms can prevent these issues from occurring in your vehicle and harming other components, your safety, and the performance of the engine.

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What is a car battery?

When it comes to the proper functioning of your car, the car battery is by far one of the most important internal components. The last thing any driver wants is to be left stranded on the side of the road with a dead battery. The battery is the power and the life of your car – without it, you wouldn’t be able to drive anywhere.


The car battery provides the necessary electricity to power every single one of the electrical components within your vehicle. Without the battery power from the car’s internal battery, no electrical component will work, like the lights, dashboard lights, or power windows. 


The chemical reaction occurs in the battery system, transforming the chemical energy into the electrical energy necessary to deliver the right amperage of voltage to the starter. In addition, the battery stabilizes the voltage to keep your engine running. Without the battery, the car would not have the energy required to start and maintain the power to run your vehicle. 


When looking at the signs of a bad car battery vs. alternator, it is important to keep in mind the varying functions that each component has in your vehicle. 

What is an Alternator?


The alternator generates electrical power and is a huge part of the vehicle’s charging system. Almost all cars with an internal combustion engine contain an alternator as well. When the engine in your car is running, the alternator’s job is to maintain a proper charge in the battery and supply electric power to the vehicle’s electrical systems. The alternator is connected to the engine and is controlled by a drive belt. If the alternator doesn’t charge, then the engine won’t work properly.


An alternator is typically a unit that doesn't require any maintenance. In some cars, it can last for as long as a decade without any necessary repairs or maintenance required if the alternator is still charging. If the alternator does fail, the car can sometimes still run for a limited time on just battery power. However, once the alternator stops charging, the engine will stall and fail. 

Signs of a Bad Alternator


There are common signs and symptoms that you should notice to properly diagnose what part of the charging system or alternator you need to replace when figuring out the signs of a bad car battery vs. alternator. 


  • Dashboard Battery Light


The most common sign there is a problem with your vehicle’s charging system is an icon will light up on your dashboard, usually in the symbol of a battery. The word “CHARGE” might also come on. Typically, this warning light comes on when you turn the ignition and then disappears when the engine is started. If it remains illuminated, then there is an issue with your alternator charging system. 


The charging system light doesn’t necessarily mean you have a failed alternator, but it does mean there’s an issue with your vehicle’s charging system. However, your mechanic will be able to determine if this has to do with the signs of a bad car battery vs. alternator or with the charging system itself. 


  • Headlight Brightness Issues


Another bad alternator symptom when looking at signs of a bad car battery vs. alternator is the dash lights and headlights will get lower when your car is idling but become brighter when you rev your engine. This means that you could have a weak alternator or a damaged battery terminal connection. You could also have a loose drive belt, which would result in a lack of power provided to the alternator.


  • Loud Noises


If you hear loud noises when your alternator is running, then the belt or pulley is usually the problem. The belt could be misaligned with the pulley, causing them not to work properly together and enhance the parts’ excess friction. If the noise continues after replacing the belt, then you need to replace the alternator to prevent the signs of a bad car battery vs. alternator. 


  • Slow Engine Cranking


When the alternator is damaged, the car’s engine will crank very slowly. In order to diagnose this issue, you need to check the ignition system before making a decision. The inability to crank might also be paired with loud noises due to a worn-out drive belt, causing the signs of a bad car battery vs. alternator symptoms. 


  • Alternator Voltage Leak


The alternator plays a vital role in converting currents from the alternator into a direct current. Over time, the electricity within the alternator can run out, causing dimming lights. We recommend using a voltmeter to ensure there are no leakages.

Signs of a Bad Car Battery

Although some signs of a bad car battery are similar to that of a damaged alternator, some distinct differences can help you when troubleshooting and diagnosing the symptoms you are experiencing in your vehicle. 


  • Dim Headlights


If you find that your headlights are dim all of the time and do not get any brighter when you rev your engine, this is due to a dying battery that will soon be completely dead. When comparing the signs of a bad car battery vs. alternator, in this situation, the lights will not get any brighter after you drive your car and will stay at a suboptimal brightness for the entire drive.


  • Key Clicking Sound


When looking at the signs of a bad car battery vs. alternator, clicking sounds while you turn the key in the ignition is a sure sign of your vehicle’s battery issues. When you turn the key, the battery sends an electrical current to the starter solenoid to power up the vehicle. If the battery is dead, the solenoid will not receive the signal, and the starter will have less power to run the car.


  • Slow Cranking


Similar to the bad alternator symptoms, slow cranking is usually the warning sign that your car is about to die. If you notice this sign in your car when looking at the signs of a bad car battery vs. alternator, this is a vital symptom that your car battery is almost dead and needs to be repaired or replaced before your car dies completely.


  • Backfiring


Luckily for you and most drivers, this is a warning sign that is nearly impossible to miss. When comparing signs of a bad car battery vs. alternator, this is a sign that you can directly attribute to the battery, showing you what part is at fault. A failing battery can cause intermittent sparks, leading to fuel build-up within the cylinders and causing engine backfiring. 

How To Determine if it is a Bad Car Battery vs. Alternator


When figuring out if the signs of a bad car battery vs. alternator originate from what exact part in your car, you need to follow two key steps to analyze and diagnose the problem.


  • Check the battery


The first step in determining where the problem is coming from in your car is to check the battery. Sometimes it depends on what environment you live in – if you live in cold weather, the battery is susceptible to dying and not starting in freezing temperatures. You can determine if this is the issue by checking the battery gauge on the dashboard.


After this, check the connections, like the electrical components and the brake lights, and clean any corrosion to see if that has caused a contaminated battery. If the battery still has not started, check the battery with a voltmeter to determine the reading. If the reading is not optimal, you might be looking at the battery as the culprit when determining the signs of a bad car battery vs. alternator. 


  • Check the alternator



If you find that the battery is working correctly, then the next step is to test the alternator to ensure it can start the battery at the right time. You can do this by running your car and unplugging the positive connection of the battery. At this point, if your car stops, you have a problem with the alternator. In this situation, when looking at the signs of a bad car battery vs. alternator, you have discovered that the alternator is at fault.



When looking at the most common signs of a bad car battery vs. alternator, both parts have different warning symptoms that can alert drivers to future car issues. If you notice the dim headlights, a key clicking sound, backfiring, and slow cranking, then your battery is at fault. If you notice loud noises and an alternator voltage leak, then you could be looking at a necessary repair or replacement for your damaged alternator. 


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