New Alternator & Battery: Light On & Car Dies [Fixed]

The main reason that the battery light comes on even after replacing the alternator and battery is the replacement parts are faulty. Yes, it’s highly like that either the alternator or battery you replaced is bad.

So, replacing the damaged component again with a functional part will solve the issue.

new alternator & battery but battery light on and car dies

Apart from that, there are many other reasons that can cause this issue. The most common ones are:

  • Loose or corroded battery terminals.
  • Malfunctioning voltage regulator.
  • Improper Installation.
  • Worn out serpentine belt.
  • Wiring issues.
  • Bad ground.
  • Accessory load.
  • Blown fuse.
  • Parasitic battery drain.

We’ll discuss all these issues in detail along with their fixes in this guide. So, without further ado, let’s dive in!

What Does The Battery Light Mean?

Before delving deep into the issue, let’s understand what the battery light actually represents. It’ll help you understand whether the issue is with your electrical system or not.

When you see the battery light coming on, it means that your battery isn’t being charged at the correct voltage. The major culprits here could be either the alternator or the battery.

battery light meaning

You’ll most likely notice other issues with the electrical system when the battery light comes on. For instance, the power windows will become slow, and certain electrical components may not turn on.

A battery light that blinks isn’t normally a serious issue. It represents that the problem is at an early stage. It would even go away on its own many times. But if the light stays lit, that’s when you have a real problem.

Our recommendation is to diagnose the issue even when you have a blinking battery light. You can address the problem early on by doing that. If you’re reading this article, it’s probably already too late to do that.

But don’t panic just yet. We’ve covered everything you need to know to fix your car’s electrical issues in this guide. Keep on reading.

New Battery & Alternator But Battery Light Comes On & Car Still Dies [Reasons + Solutions]

Keep in mind that it’s normal for the battery light to stay on for a while after you’ve changed your battery and alternator even if everything is fine. It’s not an issue at all. Your car’s ECU needs some time to adapt.

If you want to expedite the process and reset the battery light faster, you can do it with the help of an OBD2 scanner. But if the battery light comes back or stays on even after a significant time has passed, there’s a serious issue with your car.

Especially, if the battery light is solid and stays on instead of flashing. Here are the main reasons behind the battery light being on even after replacing the battery and alternator.

1. Faulty New Battery

We hate to break it to you but chances are that the new battery you got isn’t a good one. There are so many refurbished batteries that can be found in the market. It’s possible that your dealer tried to pull a trick on you and handed you a bad battery.

faulty new battery

More often than not, the battery or the alternator will be the main culprit behind the battery light coming on and your car dies. That’s why your battery light is still on even after replacing the battery. Check out both the battery and the alternator before looking into anything else.


Before you call your local mechanic a cheater, you should test the hypothesis and perform a load test on your battery. The results will reveal if you have a faulty battery.

testing a car battery

You’d need a multimeter to do the test. Follow these steps to test the battery:

  • Turn on the headlights and keep them on for a couple of minutes.
  • Turn on the multimeter and set it to DCV. Make sure you set it above 15 or around 20 DCV.
  • Connect the red lead of the multimeter to the positive battery terminal and the black lead to the negative one.
  • Collect the reading that’s displayed on the multimeter.

A reading that’s around 12.6 volts shows that you have a good battery. Anything under 12 volts or above 13 volts at this stage means that you have a bad battery.

If you see a reading close to that, everything is good with your battery so far. It shows that the battery is capable of holding the charge. But it could still lack the Cold Cranking Amps required to start the car.

Start the car with the multimeter attached to the battery. The voltage should slightly drop and will go back up to more than 13 volts. That’s because the alternator charges the battery. If that happens, your battery is fine.

If the voltage drops below 10 volts, that means you have a faulty battery. If it’s at 5 volts or even lower, then it’s totally done at that point and needs to be replaced right away.

If your car is dead instead of just having the battery light turned on, an alternative to doing this test is to jumpstart your car. If your car runs normally when you do that, it means you have a faulty battery.

If you can conclude that you have a bad battery, you need to replace it. Take it to your dealer and tell him you found out that he pulled one over you. See if confronting him solves the issue and he replaces your battery. If that doesn’t work, then change your mechanic and don’t go back to that place ever again.

It’s good to get a battery from a reliable store. Don’t buy it from just about anyone to save a few bucks. When you buy this new battery, perform a load test on it and double-check that everything is okay.

If you don’t trust the mechanics anymore and want to replace the battery on your own, we got your back. Follow these steps to do it:

  • Start by disconnecting the negative terminal of the battery first.
  • Then, remove the positive terminal.
  • Make sure you do it in that order. If you remove the positive terminal first, it can create a spark.
  • Lift the old battery and put the new one in its place.
  • Connect the positive terminal and then, the negative terminal.
  • Put some silicone grease on the terminals to preven them from being corroded.

So, now you know that replacing the battery isn’t a complicated job at all. Get the right battery for your vehicle in terms of the CCA and grip size. If you do that, the replacement job should go fine.

2. Defective New Alternator

You think you got a new alternator and installed it in your car. But is that really what happened? With an influx of rebuilt alternators in the market, there’s no guarantee that you got a new one.

defective new alternator

Even new alternators can be defective at times. As unlikely as it sounds, a bad alternator is something you should diagnose before moving on to other issues.

The next thing to keep in mind is whether you got the alternator of the right size. Not all alternators are equal. Different alternators generate different levels of current. If you got an alternator that is undersized for your car, it could be the reason why your car’s battery light is on.


Inspecting your car is the most conclusive way you can determine whether you have a bad alternator or not. You can easily do it with a multimeter. Follow these steps to do it:

Steps 01 – Connecting The Multimeter

  • Switch off your car and wait for the engine to cool down.
  • Connect the red probe of the multimeter to the positive battery terminal and the other one to the negative battery terminal.
  • Select the DC voltage option in the multimeter.

Step 02 – Collecting The Data

  • Start the engine and let it idle at 1500-2000 RPM.
  • Collect the readings of the multimeter.

Step 03 – Analyzing The Data

Once you get the data from the multimeter, you can confirm if you have a bad alternator. If the reading is between 13.5 volts and 14.5 volts, it means your alternator is fine. But if the reading is far apart, you have a faulty alternator.

You can use an OBD2 scanner if you don’t have access to a multimeter. Do you have the check engine light on along with the battery light? If so, there is a high chance that you have a defective alternator.

Connect the scanner to the diagnostic port of the error code. Look out for the error code P0562. If it comes up, it points to a bad alternator.

Check the oxygen sensors and make sure they are fine. Issues with them can also trigger this code. If there’s nothing wrong with the oxygen sensors, you have a faulty alternator.

If the diagnosis reveals that your alternator isn’t generating enough voltage, you need to replace it. It doesn’t matter whether you have a faulty or undersized alternator.

replacing the alternator

Replacing it is the only solution. Here are the steps to replace the alternator on your own:

Step 01 – Loosen The Serpentine Belt

  • Disconnect the battery ground cable from the terminal.
  • Take a picture of the serpentine belt so that you know how it goes over the different pulleys before you remove it.
  • Loosen the belt tensioner by adjusting the belt tensioner pulley.
  • Remove the serpentine belt from the alternator. There’s no need to remove the belt entirely.

Step 02 – Remove The Alternator

  • Remove the voltage regulator connector from the back of the alternator.
  • Disconnect the positive cable of the alternator.
  • Unscrew the nuts and bolts that secure the alternator in its position.
  • Locate and remove the alternator’s lower mounting bolt.

Step 03 – Replace The Alternator

  • Lift the old alternator from the vehicle.
  • Put the new alternator in the position of the old one.
  • Mount the nuts and bolts one by one by reversing the steps above to complete the installation.

So, that’s how easy it is to install the alternator on your own. If you think it’s a hard job and you can’t do it on your own, hire a mechanic. Double-check that you’re getting a good alternator this time.

3. Loose Or Corroded Battery Terminals

If you’re sure that both your battery and alternator are fine, the next thing you need to check is the battery terminals. If they are loose or corroded, all hell can break loose in your car’s electrical system.

loose or corroded battery terminals

Inspect the battery terminals of your car with your eyes. If there’s a formation of a greenish substance on it, that’s corrosion. Don’t attempt to touch it with your bare hands while your car is on.

The connection between the wiring of the battery and the terminals can also be loose. The battery won’t work properly either when that happens. Make sure you check that too after turning the car’s power off.


You can clean the battery terminals if they’re corroded. A mixture of equal parts baking soda and water should be good enough to do the trick. Take a brush and rub it all over the corroded area.

The other options for cleaning are using grease or dedicated battery terminal cleaners. What you choose is up to you. All of them are capable of doing the job. If the connections at the terminals are loose, make sure you tighten them to solve this issue.

4. Voltage Regulator

The alternator needs to power the battery at a certain voltage. If that doesn’t happen, the battery won’t get charged and there’ll be issues with the electrical system. This job is carried out by the voltage regulator.

alternator voltage regulator

It controls the voltage in the car and makes sure that the alternator produces electricity at the right voltage. Ideally, it’s between 13.5 and 14.5 volts. When the voltage regulator goes bad, the electrical components won’t get any power from the alternator.

The battery won’t get charged either. It’ll start to get depleted soon to provide power to the electrical components. So, the battery light can come on in those cases. When the battery eventually runs out of charge, the car will die.


There is no repair for a faulty voltage regulator. Depending on your car, the voltage regulator can be built into the car or it can be a part of the alternator.

Check your owner’s manual or take your car to an experienced mechanic to find out what type of voltage regulator you have. Then, you’ll have to replace it if you want a permanent fix.

5. Improper Installation

Believe it or not – sometimes, mechanics can mess up the simple job of installing batteries and alternators in a car. Not securing the connections between the alternator and the battery is one way to do it. They can also leave the connection loose at the battery terminals.

However, they can create a colossal mess at times by installing the battery backward. Your alternator can even end up smoking in those cases. However, it can also happen due to other issues with the alternator. Check out our guide on alternator smoking with the battery hooked up if you’re interested.


The solution is simple – the installation mistake needs to be corrected. If the battery was installed backward, it has most likely been fried. It’ll need to be replaced. If other installation mistakes were made, that’ll have to be fixed.

6. Worn Out Serpentine Belt

If you know at all how alternators work, you’d be aware that they convert mechanical energy into electrical energy. The serpentine belt plays an important role in creating mechanical energy.

There are many other names for the serpentine belt. It’s called a timing belt, drive belt, and even an alternator belt. So, don’t get confused if you see any mechanic using that term.

worn out serpentine belt

If you replaced both the car battery and alternator, it’s likely that something could be wrong with the serpentine belt. This belt is in constant rotation when you drive your car. So, they’re subject to heavy wear and tear. They can also snap out of their position and even break at times.

When they’re out of order, the alternator will no longer work properly. That’s how the battery light comes on. The most notable symptom of a bad drive belt is squealing noises from the alternator.

But you don’t have to do any guesswork when it comes to diagnosing a bad drive belt. Inspect it visually and see if it’s damaged. Use a flashlight if you have to so that you can properly check the grooves in it.


You have to replace the serpentine belt when it’s damaged. Make sure that the new serpentine belt you’re getting is the right replacement part for your car. Both of them need to have the same tooth shape, thickness, and diameter.

The belt also has to be adjusted in the right position to create the perfect amount of tension. If it’s misaligned, the alternator won’t work at full capacity and even that can lead to electrical issues. As it needs to be done correctly and requires expertise, it’s a good idea to hire a mechanic for this job.

7. Wiring Issues

There are so many electrical components in your car. Theoretically, wiring issues with any one of them can affect the alternator and battery. If any of the wires have shorted, it can mess up the electrical system and make the battery light come on.

car wiring issues

Apart from shorting of the wires, any of the wirings can also be loose and cause the same issue. Give more attention to the alternator wiring as the culprit would often be there.

Generally, there are four wires leading from the alternators in modern cars. Two of them connect to the battery. The third one gets the signal of how much current to generate. The fourth one powers the field coil.

Check each of them and make sure the connections are nice and tight. The mechanic may have also connected the alternator cables to the wrong battery terminals.


If you find any of the wirings to be loose, you need to tighten them. If that solves the issue, you’re done. Make sure that the alternator cables are connected to the battery terminals properly.

The red clamp goes to the positive terminal and the black one goes to the negative terminal. If any of the wirings has shorted or been damaged, it’ll have to be replaced.

8. Bad Ground

It’s highly important that all the required components in the car have proper ground connections. Having secure ground connections makes the excess electricity flow to the ground. Thus, it ensures the safety of all the electrical parts in your car.

However, if the ground connections are loose, it can wreak havoc on the entire electrical system. The ground connections can also be damaged and cause this issue. Start by checking the battery and alternator ground connections.

If the connections are good, then the issue can be with any of the other electrical components. Diagnosing them can be extremely difficult and may require professional help. The battery light can come on due to bad ground and keep the car from starting.


If you have loose ground connections due to corrosion, you have to clean the area of the connection. It can also be the result of negligence and just leaving the connections loose. You have to tighten them in that case. If the ground wires have been damaged, you need to replace them.

9. Accessory Load

There are so many electrical accessories in modern cars. Many of them draw their power from the alternator when the vehicle is on the move. On top of that, the alternator also has to charge the battery.

car accessory load

So, the job of the alternator to keep charging the battery and powering the other components at the same time becomes incredibly hard. So, the alternator won’t be able to charge the battery as much as required.

The battery will also lose its charge to power the different components when the alternator fails to do the job. So, 


Of all the issues we mentioned so far, this one is the rarest. But that doesn’t mean it can’t happen. If you think you have turned on too many electrical components at once, just step back and turn some of them off.

You don’t need to be using all of them anyway and put any unwanted load on your vehicle’s charging system. The battery light should disappear after a while if using too many electrical components had been causing the issue all along.

10. Blown Fuse

If your car dies even before replacing the alternator and battery with new ones, the first thing you should do is make sure that the replacement parts are okay. If you did that, look at the fuses next.

 car blown fuse

Especially, check the alternator and battery fuses. Locate them in your fuse box. Check if they are blown. A visible gap between the wires inside the fuse means that the fuse is blown.

If any of the two fuses is blown, that explains why the battery light comes up in your car. As the alternator quits working due to the blown fuse, the battery stops getting charged. So, the battery light pops up.

Eventually, the battery runs out, and the car dies and won’t start. You can swap the blown fuse with a good one that has the same amperage rating. If the car works fine after that, you can conclude that the fuse is the main issue that’s causing all these problems in your car.


You’re lucky if the problem is a blown fuse. Because you can easily replace it with a new one. It’ll be a cheap replacement. All you need to do is pull out the old fuse and replace it.

Make sure the new fuse has the same amperage rating as the fuse you’re replacing. It’s a good idea to check all the fuses in your car with a circuit tester to make sure the other electrical components will work properly.

Keep in mind that a blown fuse is the result of electrical overload. So, there may be an underlying problem behind it. If replacing the fuse solves the issue, don’t worry about it. But you’d have to diagnose the main reason behind it if the fuse keeps on blowing.

There are also fusible links between the battery and the alternator in some cars. They act just like the fuse and get broken when there’s a high level of electricity. If your car has that and the link is broken, replace it.

11. Parasitic Battery Drain

There’s always the possibility that a part in your car is staying on even when you turn off the key to your car. The main reason behind it could be due to a shorting of the wires of such electrical components.

It can be anything ranging from the interior lights to the trunk. When the component remains on, the battery continues to supply power to it. Eventually, it runs out of charge and the car dies. It won’t start and you’d often have to jumpstart the car to be back on the road.


The first thing you have to do is to inspect the car and see if there’s the possibility of a parasitic drain. Wait till the end of the night and see if any of the lights have come on.

Tracking all sorts of parasitic drains aren’t that obvious. Sometimes, you’ll need the help of mechanics to do it. But if you want to it on your own, follow these steps to identify a parasitic draw:

  • Unscrew the negative battery cable.
  • Move the positive cable of the multimeter to the DC Amps spot.
  • Turn the multimeter to the DC Amps as well.
  • Connect one lead of the multimeter to the post and the other one to the cable. Check this picture below to see how it’s done:
testing parasitic drain

You’ll get a reading on the multimeter. Ideally, you want the reading to be 0.05 amp or less. A little higher is okay as shown in the picture above. If you have a reading that’s 0.1 amps or higher, then you have to be concerned.

Wait for at least 15 minutes to half an hour to see if the readings changed at all. If they didn’t your car is fine. But assuming that you have gotten a bad reading that’s above 0.1 amp, the next challenge is to find the culprit that’s causing the issue.

The draw can occur from anywhere. So, how do you find where it’s coming from? Get to your fuse box and pull them one by one. Whenever pulling a fuse affects the reading of the multimeter, you’ve found your culprit.

Once you find the faulty component that’s causing the issue, you may have to replace it or the wiring attached to it. Once you do that, your car should run normally again.


How do the battery and alternator work together?

The battery provides the initial power required to start a car. Once the vehicle is up and running, the alternator takes over and powers the electrical system. It also charges the battery at the same time.

Can a dead alternator drain the battery?

When an alternator dies, it doesn’t charge the battery anymore. The electrical components of the car run solely on battery power. So, the battery gets drained and the car dies after using all the power from the battery.

Is it okay for the battery light to come on when you start the car?

Yes, the battery light is supposed to come on when you start your car. A bunch of other lights would also come on at the same time. But it should go away after you’ve driven for a while. 

How often do I need to replace the serpentine belt?

You have to replace the serpentine belt when it goes bad. Serpentine belts that are low in quality generally don’t last longer than 30,000 miles. But if you get high-quality ones, they’ll last for at least 50,000 miles or more.

Should you drive with the battery light turned on?

If it’s blinking, you can do it but refrain from it if the light is solid. Even if you’re driving with it, get to a safe space ASAP and stop the car. You may be running on battery power and the car can come to an abrupt stop anytime.

Can I jumpstart my car if it has died?

Yes, it can work if the battery was dead. If jumpstarting the car restarts your car, you can be sure that there’s an issue with the electrical system. It’ll most likely be the battery or the alternator.


Replacing the alternator and battery generally solves the electrical issues in your car. If you’re so unlucky that your car dies even after installing a new battery and alternator, it’s normal to be disappointed.

The first warning sign of problems with your electrical system is the battery light coming on. When the matter gets worse, the car can die. Hopefully, you’d be able to solve the issues after completing this guide. Comment below if you have any more questions about car batteries and alternators.

About John M

John contributed as a technical head at an automobile company just 2 years after his post-graduation in Automobile Engineering. He loves to lead a free life, so he left his job & started blogging. Now, he does research on every automotive problem, part & product and seeks a better solution & best products & shares his findings with his readers to help them as well as to minimize their struggle.

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