Car Shuts Off When Battery Is Disconnected [How To Fix]

The main reason your car shuts off when battery is disconnected is a faulty alternator. The car is supposed to run with the power from the alternator when the engine is running. But if the car dies in that situation, it’s certain that you have a bad alternator.

car shuts off when battery is disconnected

I’ll walk you through how you can fix this issue in detail in this guide. On top of that, you’ll also learn why the car battery gets disconnected when you’re driving and what you can do to solve it. So, let’s dive in!

Car Shuts Off When Battery Is Disconnected [How To Fix]

If your car battery gets disconnected with a running engine, it’s never good. It’s an unsafe situation as there will be voltage spikes due to that. The different electrical components will be subject to those voltage spikes and they can easily get damaged.

disconnected the car batttery

The voltage spikes will be even more severe if it happens when you’re driving. It’s almost certain that some electrical components will go bad in such cases. It’s certainly happened to me once my car battery got disconnected. So, you should never voluntarily remove a car battery from a car engine.

While it’s okay for some parts to go bad, your engine should still be running if the battery gets disconnected. That’s because the alternator produces the power to run the electrical parts once you start the engine.

So, the battery getting disconnected shouldn’t prevent the car from running. But if the car dies and the engine stops, it’s a dead giveaway that you have a weak alternator.

In that case, you have to restore the battery connection first. Hopefully, that’ll solve the problem in the short run. But for a more long-term solution, you should replace the alternator.

How To Replace The Alternator In A Car?

If your car dies when the battery gets disconnected, you have a bad alternator. You’ll have to replace it. Thankfully, replacing the alternator is an easy job that you can carry out on your own.

Even if you have no prior experience in replacing alternators, there’s nothing to worry about. I got you covered. Follow these simple steps to replace the alternator on your car:

Step 1 – Follow Safety Precautions

Before we get into the nitty gritty details of replacing an alternator, it’s important that you remain safe. Set the parking brake and make sure the automatic transmission is in the park. You should also set the manual transmission to neutral.

Wait for the vehicle to cool down to avoid any burns when you’re doing any repairs. As you’ll be working on the engine, make sure you wait for the car to cool down. Avoid wearing any loose clothing that can fall in the car.

Even if you wear any jewelry that gets caught in moving parts can bridge electrical connections. Finally, wear eye-protective goggles to avoid the side effects if there are any potential sparks.

Step 2 – Test The Battery

It’s important that you test the battery before you remove the alternator. That’s because the alternator maintains the charge of the battery but doesn’t improve it. So, if you replace the alternator while you have a bad battery, the new alternator will also start to fail in time.

test the car battery

Test the battery using a multimeter. If it reads around 12.6 Volts, it’s a good battery. If it’s less than 12.4 volts, it needs to be recharged. You can take the car to a local Autozone for free testing and charging. Make sure that the battery is fully charged before you proceed to remove the alternator.

Step 3 – Remove The Alternator

If you’re sure that your battery is charged well, you need to disconnect the ground cable of the battery. Then, the rest of the removal process will depend on your car.

According to the location of the alternator in your car, remove anything that could get in the way of you removing the alternator. There are some components like heat shields that could be troubling you. So, remove them and disconnect the electrical cable from the alternator.

Remove the drive belt from the alternator pulley. Then, remove the mounting bolts that secure the alternator in its place. Usually, there would be no more than 3 bolts for most cars. Once you remove the bolts, the alternator will be isolated. You can easily pull it off at that stage.

Step 4 – Inspect The Removed Alternator

Once you’ve taken off the alternator, you should check it. Sometimes, the alternator goes bad due to other issues. If you don’t correct these issues, the new alternator will also go bad quickly. So, check the alternator to spot what these issues could be.

check the alternator

First of all, check if there is any liquid on the alternator. If there’s any contamination on the alternator, it indicates that fluid could have leaked into it. Usually, coolants or engine oil leaking into the alternator will cause this issue. If you see that, you need to fix the leak.

Secondly, look for burned areas in the alternator. That’s a sign of an overheated alternator. It typically happens when the charging system is under a lot of pressure due to aftermarket radios or other high-powered components.

Such components could be the lighting or other electric accessories. Those parts could have a high power requirement and that would have an impact on the alternator. The battery being bad can also overheat the alternator. So, inspect these issues and when you find the issue, fix it.

Finally, spin the alternator pulley. If you can’t spin it easily, a bearing inside could have failed due to normal wear and tear. But if it hasn’t been too long since you installed the last alternator, it could be due to an overtightened belt. 

In that case, you’d have to lower the tension on the belt after installing the new alternator. If there’s any glazing or signs of wear and tear on the belt, it’s a good idea to replace it altogether.

If you notice any of the issues that I mentioned, fix them first before you replace the alternator. Otherwise, the new alternator would also go bad soon and the replacement won’t make any sense.

Step 5 – Replace The Alternator

Make sure your new alternator matches the old one and the mounting bolts go in the same places. Once you check that, put the new alternator in place of the old one. Then, simply reverse-engineer the steps you took when removing the alternator to install the alternator.

Don’t overtighten the electric cable when you connect it to the alternator. If you apply too much pressure, you can break the electric components. Similarly, don’t overtighten the mounting belts.

Make sure you adjust the belt to the specifications recommended by your car manufacturer. That’s how you can replace the alternator. If you don’t feel comfortable doing it yourself, you can hire a mechanic for this job.

After replacing the alternator, do a quick check again. Double-check that the wires are tightened and nothing is loose. Start the car and ensure that the alternator is running. If everything is okay, congratulations on replacing the alternator successfully.

Why Does Battery Get Disconnected When You’re Driving?

It’s not normal for the battery to get disconnected when you’re driving. There are a few reasons why your car battery keeps disconnecting. So, it’s important to know how you can solve these battery issues whenever they occur. Here are the top reasons why your battery gets disconnected and how you can fix them:

Corroded Battery Terminals

When there’s corrosion in the battery terminals, the battery won’t make a proper connection. So, it can get disconnected when you’re driving.

corroded battery terminals

So, you’d have to remove the corrosion to solve this issue in the long run. Follow these steps to do it:

  1. Switch off the engine and wait for some time to let it cool down.
  2. Disconnect the battery terminals from the battery posts.
  3. Clean the battery terminals with your preferred tool. You can choose a weird brush or battery terminal cleaner for this job.
  4. Once you’ve removed the corrosion, reconnect the battery terminals to the posts.
  5. Add some grease to the battery posts to prevent the terminals from getting corroded again.

Loose Battery Terminals

The battery terminals must be connected tightly to the battery posts to secure a tight connection. If the connection is loose, the battery can get disconnected. The good news is that it’s incredibly easy to check if the connection is loose.

Just wiggle the terminals a little bit and see if you can move them from side to side. If you’re able to lift them from the battery posts, then you can be sure that you have a loose battery connection.

The fix is simple. Just remove the battery connections and tighten them firmly this time. You can also use battery shims or battery sleeves to make a tighter connection if they’re loose.

Fried Battery Cables

The battery cables could go bad due to old age or damage by rodents or other animals. It’s an annoying issue but you can fix this issue by replacing the battery cables.

It’s not just me who thinks these are the main issues that disconnect the battery in the middle of driving. According to Axiya, the reasons I talked about are also the top reasons behind the battery getting disconnected while driving.

How To Prevent The Battery From Getting Disconnected When You’re Driving

You already know the main reasons why your battery could get disconnected when you’re driving. So, you can keep this issue from occurring again by taking good care of your battery.

Proper maintenance is the key to not only preventing it from being disconnected but also making sure that it lasts a long time. Here are some of these overall maintenance tips you should follow to keep your car battery in an optimal condition at all times:

  1. You have to ensure that the battery connections are tight. Inspect the battery at periodic intervals and see if the connections are getting loose. If they are, just tighten them again.
  2. Clean the battery posts and battery terminals from time to time. Corrosion is one of the main things that makes a battery go bad. So, if you clean them, the battery won’t get corroded and you will be able to use it for a long period.
  3. Make a habit of turning off the engine and accessories when you’re not driving the car. When you’re idling, the battery loses charge when running the electric components. So idling will severely shorten the lifespan of a battery.


Is it okay if the car dies when removing the positive battery cable?

No, the car dying when you remove any of the battery cables is a sign that you have a bad alternator. Even in that case, you’d have to replace the alternator and tighten the battery connection.

Is disconnecting the car battery while driving a good way to test the alternator?

No, removing the battery while driving can create voltage spikes and damage the electric components. So, test the alternator with a multimeter like a normal person. You can also take your car to a local Autozone to get it tested.

What are some loose positive battery terminal symptoms?

The first sign that you have a loose battery connection is that the battery light will come on. If you see that, inspect your battery right away. If any of the connections are loose, tighten them to fix this issue.

Why does my car keep shutting off after I replace the battery?

The main reason behind it is a bad installation job. The memory in the computer of the car gets erased and that’s what creates this issue. Eventually, the car will relearn the settings and your problem will be solved.


Now you know why the car shuts off when battery is disconnected and how you can fix it. The first thing you should do is reconnect the battery and then, replace the alternator.

I’ve shared with you in detail how you can do all these things. You may still be left with questions about what else happens when the battery connection is removed. Check out our guide on battery getting disconnected explanation to learn more about it in detail.