Bad Car Battery vs Bad Alternator: What’s The Difference

1 What Are The Signs Of A Bad Car Battery?

The function of a car’s battery is to provide current to the engine and other accessories when the engine is not running. However, when the engine starts, the alternator provides current and charges the battery as well. Since both the battery and alternator are parts of your car’s charging and starting systems, identifying the problem can be challenging. Here are some symptoms of a bad car battery.

1. Dim Dashboard Lights Or Headlights

When the vehicle is turned off, the battery supplies energy to all the electrical accessories, like headlights,windshield wipers, and automatic windows. You can check the battery’s health by simply turning off the engine, leaving the ignition on, and observing if the dashboard lights are on. If the dash lights or headlights are dim, low, or completely turned off, the car’s battery has little to no charge left.

2. Weak Engine Start Or No Start

If your engine won’t crank or struggles to start and takes a long time, your battery might be the culprit. When the car is started, the engine starter uses the current from the battery to crank the engine. If you face a condition where the engine cannot start, it’s time to jump-start your vehicle using jumper cables. If the problem persists, that means the battery cannot hold a charge and has to be replaced. However, there can be various reasons why a car won’t start.

3. Battery Corrosion

Corroded battery terminals impede electrical energy, preventing the car battery from receiving a proper charge. Your car’s alternator produces electrical energy to charge the battery when the engine is running. This electrical charge can be hindered if the battery terminals are corroded or have deposits. This will drain the battery making it difficult to start the engine, and eventually, the battery has to be replaced.

4. It’s An Old Battery

A conventional car battery lasts 3 to 5 years. Over time, the battery becomes weak and loses its capacity to hold a charge because the metal inside corrodes. Eventually, the battery becomes so weak that it can’t supply the proper current to start the vehicle. To ensure you do not run into a similar condition, replace your car’s battery at recommended intervals and follow proper battery maintenance.

5. There’s An Odd Smell

A leaking lead-acid battery can release sulphuric gases, emitting the odd rotten egg smell. A battery may leak due to several factors, like damage to its body, overcharging, and cold weather. If your car battery is leaking, it should be replaced as soon as possible.

6. Swollen or Warped Battery Casing

Another sign of a failing or bad car battery is if it’s swollen or warped. Extreme temperatures can cause a battery to swell as internal parts expand, causing your car battery to bloat or distort. This can also occur if the battery is overcharged or exposed to very cold temperatures. A faulty regulator can frequently overcharge your vehicle’s battery.

2 How To Replace Your Car’s Battery?

Replacing your car’s battery is another part of routine vehicle maintenance because a car battery usually lasts around 3 to 4 years. No matter how you treat your vehicle, batteries run out of charge and have to be replaced. However, if your alternator is fine, and the battery is the culprit, follow the simple step-by-step method below to replace your car battery at home.

1. Turn off your car, remove the key, and park it on a level surface. 

2. Before you locate the battery, make sure the engine has cooled down. While most cars have batteries mounted on the front on a plastic or metal tray, some vehicles have them in the rear. Refer to your owner’s manual for a better understanding. 

3. Locate the battery terminals. Usually, they are covered by a plastic cover, and the terminals are colored black and red (negative and positive, respectively). Terminals are also marked with “+” or “-” signs for easy identification.

4. Proceed by disconnecting the negative terminal first. Use a wrench to loosen the bolt that tightens the terminal. Once loose enough, rotate and shake it to disconnect it completely.

5. Once done, secure the terminal with a zip tie and disconnect the positive terminal as well.

6. Loosen the metal plate and set the old battery aside. Car batteries have a caustic liquid in them. Make sure you always keep it upright, as spilling it can be hazardous.

7. With the help of a battery cleaner and a wire brush or sandpaper, clean the terminals well until you can see a clean metal surface. Clean the battery tray with some soapy water and a microfiber cloth. Inspect the cable thoroughly to ensure that it is not damaged or frayed.

8. Lower your new battery into the battery tray and make sure it matches the positive and negative terminals. Reattach the metal bar and tighten the bolts.

9. Connect the battery terminals by attaching the positive (red) terminal first and then the negative(black). Make sure the terminals are pushed all the way to the end. It’s always a good idea to spray some anti-corrosive battery gel before connecting the terminals.

10. Close the hood of the car and start the vehicle. If the vehicle doesn’t start after changing the battery, consult a mechanic.

3 What Is The Battery Warning Light?

There’s a misconception regarding the battery light warning; it’s time to clear that up. Your battery light does not indicate a problem with your battery, it may even come on and then go out when you start your car. But if it comes on while driving, then it’s a clear indication that your charging system or alternator has a problem. It also means that your vehicle is running only on the energy left in your battery, which will only run for a while until the lights get dim. It is likely that all the electronics will shut down, and eventually the engine too if you keep driving with the battery warning light on the dashboard. It is important to note that when the alternator fails, it can put a strain on the battery and lead to a replacement.

4 What Are The Signs Of A Bad Alternator?

If your vehicle isn’t showing any of the symptoms mentioned above, maybe your car’s alternator is malfunctioning. Apart from charging your vehicle’s battery, the alternator also regulates the amount of electric current supplied to the battery. This can cause overcharging and overheating of the battery, which can decrease the battery life. Therefore, it’s necessary to take a closer look at the symptoms of a bad alternator.

1. Dull Lights

It is common to see weak dome lights, headlights, and taillights when the alternator isn’t doing its job properly. If you notice the lights flickering or becoming very dull when the vehicle is idling and brightening as the RPMs increase, there may be an alternator issue.

2. Burning Smells

The alternator has many copper coil windings that start smelling when burnt. The alternator has neared its end if the coils burn up and produce a strong burning odor.

3. Loss of Power to Various Electrical Components

Since all the dashboard components run on the alternator, if it fails, you can notice intermittent functioning of the radio, infotainment system, GPS system, etc.

4. Warning Lights

You may start seeing “ALT,” “GEN,” or even “engine” lights on the dashboard, indicating that the alternator or battery is faulty.

5. Engine Stalling

The alternator powers the fuel pump, and if it fails completely, you may experience engine malfunctioning, which can even bring the vehicle to a halt.

6. Trouble Starting the Engine

The alternator is responsible for charging the battery, and if it fails, then the battery will lose its charge, which can hinder the starting of the vehicle. Even with a new battery, this will happen again, and the culprit is a broken alternator, not the battery.

7. Squealing or Grinding Noise

Strange noise coming from your car is never a good sign. The alternator runs on a needle bearing that is prone to failure and results in grinding noise. It receives power through the serpentine belt, which can also get worn out and stretched over time, which may create a squealing noise from the engine and eventually render the alternator broken.

8. A Dead Battery

Yes, this can be a little confusing, as this is also a symptom of a bad battery. A faulty alternator will not charge the battery, leaving it dead. If your alternator is bad, even a new battery won’t be charged, and you will witness a dead battery while starting the car engine the next time.

9. Electrical Issues

A dying alternator can lead to a wide range of other electrical issues, such as failing to deliver energy in a steady format. You can notice the headlights getting dim or even brighter than usual. Other symptoms can be the interior and dashboard lights flickering, and even the power windows can operate at a much slower pace than usual.

Once you suspect or experience these symptoms, it is necessary to diagnose the alternator to ascertain the problem at hand. This way, you can determine whether the problem is caused by the battery or the alternator. Refer to our guide on battery and alternator diagnosis.

5 How To Replace Your Car’s Alternator?

The complexity of the replacement of the alternator is dependent on its placement. Some vehicles have the alternator situated right on top of the engine, and some may have it deep down, and you might have to access it from the bottom of the vehicle. Once you have found the best position for working on the alternator, then find all these necessary tools to remove and refit the alternator:

• Ratchet
• Socket Set
• Extension
• Wire Brush
• Torque Wrench
• Serpentine Belt Tools

Steps To Change Your Your Car’s Alternator

1. Put the car in park and pop the hood. Make sure the engine is cool enough to touch and remove the negative battery terminal by loosening the bolt.
2. Now, if your alternator needs access from the bottom, hoist the vehicle on jack stands using a floor jack and remove the engine cover.
3. Make room to access the alternator properly, but do not remove the radiator hoses as that may lead to coolant leaks and AC lines.
4. Once you have sufficient access to the alternator, remove the alternator connections to it using a flathead screwdriver and a ratchet, and a small socket for the terminal connection.
5. Before you remove the alternator bolts, using a serpentine belt tool or a long and narrow breaker bar or wrench, loosen the belt tensioner that holds the alternator belt. Do not completely remove the belt unless you are replacing it.
6. Then proceed to remove the bolts that hold the alternator in place. You might need to use a breaker bar in order to free the bolts.
7. The alternator will be detached from the bracket.
8. The bracket acts as a ground for the alternator, so ensuring a good contact surface is necessary. Using a wire brush, clean the area of contact between the alternator and the bracket. Also, clean the bolts of any corrosion.
9. Now check that the new alternator is the same as the old one and verify that the mounting points are an exact match. 
10. Place the new alternator on the bracket and secure the bolts. Using a torque wrench, torque the bolts to the correct specification mentioned in the owner’s manual.
11. Attach the electrical connections similar to how they were removed, and then place the belt on the alternator pulley. If the belt is completely removed, then refer to the belt diagram to install it correctly, and then tighten the belt tensioner.
12. Reinstall any connections that were removed, and then secure the battery terminal using the bolt.