You go to start your car, but when you engage the ignition, your car won’t start — and your stomach sinks. If your car won’t start, it’s often due to a malfunction of either the battery or the alternator. If it’s one of those things, recognizing which one can be relatively simple.
Battery or alternator: what’s causing the problem?
Starting and running an engine, in its simplest form, is a 3-step process. First, the battery delivers a jolt of electricity to the starter. This starts the engine running, which puts the alternator into action. Finally, the alternator completes this cycle by charging the battery.
Using the process of elimination, find the culprit by bypassing the battery’s role and jump-starting your car. If the engine starts but dies immediately, your alternator probably isn’t keeping your battery charged. If a jump starts and keeps your car running, but the car can’t start again off of its own power, a dead battery is probably your answer.
Signs of a bad battery
Check for these common symptoms of a dead battery:
- Are the dashboard lights dim? First, check the dashboard battery gauge. The battery should be giving a charge, even while the vehicle is off. If the dashboard lights are dim, something is likely wrong with your battery. Try turning on your windshield wipers, lights or automatic windows. Then make sure these are all turned off and once again try to start the car.
- Check for battery corrosion. If it still won’t start, use a rag to carefully wipe away any corrosion on the battery and have someone jump-start it. After running the motor for a while, turn the car off. If you can’t get it to restart, this is a sign the alternator is doing its job of keeping the battery working while the motor is running, but the battery isn’t retaining the charge when the alternator has stopped.
- The car battery could be old. As batteries age, they become less able to retain a charge because the metal inside corrodes. On average, car batteries last between 3 and 5 years.  Eventually, the level of battery charge diminishes to the point where, no matter how much power the alternator gives to it, the battery can’t hold enough power to start the car. However, there are steps you can take to help preserve your car battery life.
- Your radio won’t turn on. If your ignition is in the on position, the battery should be able to run your radio, headlights, windshield wipers, and other electronic components. If you notice your radio display or headlights flickering or dimming, there’s a good possibility your battery isn’t well-charged.
- Your car starts and dies immediately. This can happen for a number of reasons, but checking your battery is the best place to start. This is an odd problem that typically will happen only on certain vehicles, and it is a result of the battery having only enough voltage to start the car.
- Your battery is swollen. If your battery is bloated, you should be able to notice thanks to manufacturer design: You’ll easily be able to identify bulging in the battery’s casing. This problem occurs when your alternator has overcharged the battery due to a bad voltage regulator.
Signs of a bad alternator
If the above steps reveal that the battery is working, it’s time to take a closer look at the alternator. There are certain bad alternator symptoms to look for. Find out how to tell if your alternator is bad¹²:
- Dim interior lights. While running the car, note the brightness of the interior lights. If the dashboard gradually dims, the alternator is likely at fault.
- Dim or overly bright headlights. Do you notice your headlights running brighter as you accelerate and dimming as you stop? This is often caused by the alternator not keeping the battery adequately charged.
- Growling noises. Did you hear a growling sound before the trouble started? That sometimes occurs before an alternator fails.
- Smell of burning rubber or hot wire. Are there signs your alternator is overheating, such as the smell of burning rubber or hot wires? If so, it’s time to replace it.
- Test the alternator. Some may recommend running the engine with the negative battery cable disconnected to test the alternator. However, this is not a good idea because it could damage the electrical system of your vehicle and cause greater problems. Find out how to test an alternator.
Can you drive with a bad alternator or battery?
While your car can run with a faulty alternator for a short period of time, doing so includes risks and can be dangerous for you and everyone else on the road. Driving on a bad alternator can cause a variety of issues in other parts of your car, including the engine and electrical components. Also, your car’s battery will deplete eventually, causing your car to die. If you don’t have the resources available to jump your car and find yourself in a remote area, this could leave you stranded. Your vehicle can also lose power on its power steering, which can result in you losing control of your car. For these reasons, it’s best to get your alternator fixed to protect yourself and other drivers on the road.³
Fixing your battery or alternator can be an expensive repair. See how you can find the right mechanic to work on your vehicle. Make sure you have roadside assistance so you can get help if your car won’t start.
 “Is your car battery dead?” autozone.com/diy/battery/is-your-car-battery-dead Accessed, February 28, 2022.
 “10 Warning Signs Your Car Battery is Dying,” valleyhondadealers.com/blog/10-warning-signs-your-car-battery-is-dying/ Accessed, February 28, 2022.
 “Can A Car Run With A Bad Alternator (Risks Of Driving With A Bad Alternator),” Jeffery Ekweghi, autovfix.com/can-a-car-run-with-a-bad-alternator-risks-of-driving-with-a-bad-alternator/ Accessed, Feb. 28, 2022.
Additional car issues resources:
- How to Avoid a Dead Car Battery
- What Is an Alternator and How Does it Work?
- When to Change Your Car Battery
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