How to Jumpstart a Car With a Broken Alternator

How to Jumpstart a Car With a Broken Alternator

Having an alternator go bad is one of the most frustrating things that can happen to a car. It doesn’t matter how many times you charge the battery; it will be dead the next time you drive your car. It will probably happen right after you buy a cartload of ice cream. Trust us, we understand just how frustrating the problem can be.

In this article, we’ll walk you through how to get your car started again so that you can limp to a shop. We’ll also look at why a bad alternator can cause problems and answer some common questions.

Jumpstarting Your Car Safely

The following steps are the steps you need to take to safely jumpstart a car. It does not matter if the alternator is bad; the steps are the same every time the battery lacks the power to start the motor.

What You Need

  • A car with a good battery or a jump start pack like one of these we recommend.
  • Jumper cables
  • A friend to help

The Process

These steps should be followed for the best results.

1. Attach the Leads to the Car With a Low Battery

Start by attaching the negative battery cable clamp to a grounding point. A ground point can be any exposed, unpainted metal or bolt attached to a motor’s ground strap. Then attach the positive cable clamp to the positive terminal on the battery.

You attach the negative cable to a ground point instead of the negative terminal because it helps you avoid accidentally touching the negative and positive sides together. Touching the negative to the positive will cause sparks or worse, and it should be avoided.

2. Press the Start Button on the Pack

If you are using a jump pack, use manufacturer’s instructions to begin the jumpstart process. Often there is a button you need to press. Then you can proceed to step 5.

3. Or, Connect the Cables to the Other Car

If you have another car with a good battery instead of a jump pack, you will need to connect the cables to the battery in the car with the good battery. While the car is off, connect the negative clamp to the negative terminal and the positive clamp to the positive terminal. It’s important to make sure you don’t touch the ends of the cables together.

Suppose you don’t have a friend to help you hold the cables or want to minimize the risk of sparks entirely. In that case, you can connect the positive terminals together first, and then connect the negative terminal of the good battery to the ground of the car needing a jump.

4. Start the Car With the Good Battery

Leaving the car off while attaching the cables adds a layer of safety to the process.

5. Let the Bad Battery Charge for a Few Minutes

Let the jump pack or the other car charge the new battery for four or five minutes. This will allow enough of a charge to build to start the car being jumped.

6. Attempt to Start the Car

Let your ears be your guide when you attempt to start the car with the bad battery. If the motor turns over slowly or you hear clicking, let the battery charge for longer instead. If you are working with a friend, have them step on the gas a little bit as you try to start your car.

7. Remove the Cables Once the Car Starts

Remove the cables carefully, so you don’t accidentally strike a moving engine part or the other cable end. Start by removing the positive terminal clamps. Once they are disconnected, there is no risk of touching the ends together.

If you are using a jump pack, simply disconnect the pack and store it in your cabin.

8. Drive to a Shop

After you close the hood, drive the car straight to where you can have it worked on, whether that’s your garage or a mechanic. A bad alternator can cause dangerous situations, like headlights going dark or your car suddenly dying, so it’s best to get to safety as soon as possible.

If you would prefer to watch the process, this video from does a good job showing the process we describe.

The Dangers of Jumping a Car With a Bad Alternator

alternator being worked on by mechanic

It may seem like the problem is solved after you jump your vehicle and it’s running. However, jumping a car with a bad alternator is more like taking aspirin after you break your leg. You feel better, but the problem is still there, waiting to ruin your day.

There are a couple of things that can happen that will cause you hours of frustration and may be dangerous to you and others on the road. That’s why we strongly suggest using a jump start as a means to get out of a bad situation and nothing more.

Your Engine Might Stop

The motor in your car needs a certain amount of voltage to run. In most cars, it’s about 12.8 volts, which is provided by the battery when the motor is off and the alternator when the motor is running. Most batteries do not have enough energy to keep a car running by themselves for very long.

In fact, your average 425CCA car battery has a reserve capacity of about 60 minutes. If it’s low, which it will be if you just had to jump it, you can be looking at as little as 10 minutes before your battery can not produce enough power to run your car. If that happens while you are driving, your car will stall and not be able to start again.

Lights and Other Electrical Systems Can Fail

Aside from the potential to end up as a road hazard, you may also need to limit your driving time with a bad alternator because you won’t have a fully functioning vehicle. Lights are an essential part of road safety, and they are one of the first things to stop functioning when an alternator can’t produce enough voltage.

Symptoms of a Bad Alternator

There are five main symptoms of a bad alternator.

  • The battery charge indicator light is illuminated
  • The headlights or other electrical systems fail intermittently
  • The car stalls after driving
  • The car has trouble starting
  • The battery is low after driving

Bad Alternator vs. Bad Battery

A bad battery can cause many of the same symptoms that a bad alternator can cause. The easiest way to tell whether or not the battery has gone bad instead of the alternator is that a car will run without issue on just the alternator. If your car has trouble starting, but it works fine after jumping it, you probably just have a bad battery.

If the car runs after a jump start, but the lights are dim and the motor stalls, then your alternator is probably bad. We have a guide here that will help you install a new alternator and get back on the road quickly.


Can You Jumpstart a Car With a Bad Alternator?

Yes, you can. It may not stay running for long, though, depending on how depleted the battery is. A battery that was only a little low may allow your car to run for ten minutes, which is hopefully long enough for you to be able to get to a mechanic.

Will a Car Run With a Bad Alternator?

It depends on how bad the alternator is. If the regulator on the alternator has gone bad, which you can learn about here, you may be able to run the car with minimal problems. If it isn’t producing any voltage, the car will run, but not for very long.

Will a Battery Die if the Alternator Is Bad?

The battery will not charge as the car is running if the alternator is bad. That means that after a certain amount of time, the engine will drain the battery to the point that there is not enough power left to run the car. Doing this repeatedly will kill the battery.

How Long Will a Battery Last if the Alternator Is Bad?

A battery may last up to ten minutes if the car is running and the alternator is bad. However, the battery may not be able to start the car again.

How Can You Tell if Your Alternator Is Bad?

There are two main ways to tell your alternator may be failing. The first is that there will be a low charge warning light that illuminates on your dashboard. The second is that your headlights may dim or flicker as you drive. You can read more about alternators and bad alternator symptoms here.

Stay Safe and Keep the Lights On

We know that it can be intimidating to have to jump your car. Especially if you need to ask a stranger in a parking lot or on the side of the road; that’s something even seasoned car gurus have trouble with.

We hope that you can use this guide to feel a little more confident and get your car to a shop where the problem can be fixed quickly and painlessly. After all, it concerns your safety and comfort, and we want as much of that for you as possible.

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