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Have you ever received a check engine warning light on your dashboard? Not aware of the real issue, you may wonder if I can drive with a bad alternator or battery as both give off similar foul signs.

A bad car battery will show symptoms like the car’s engine not starting, the car’s headlights dimming in the middle of a drive, or the car’s headlights turning on and off while driving. If you notice these symptoms, your car battery needs to be replaced. On the other hand, a bad alternator will show symptoms like the battery light coming on and staying on or your car’s engine running very slowly. If you notice these symptoms, your alternator needs some attention.

In this article, we’ll review signs of a bad car battery vs. alternator so you know what happens when something happens. So, stick around.

Signs of a Bad Car Battery

Before you set afoot for a long journey, double-check the condition of your battery. You have every reason to be cautious as the battery is the power source for your vehicle’s electrical system, producing electricity, powering the starter, and other essential systems, including lights and radios.

Most of the time, a bad car battery is pretty easy to spot. But sometimes, it can be harder to realize what’s going on. A bad battery will eventually stop working, but it might not be immediately obvious. If you see any of the following signs, it’s time to get a battery replacement service.

Battery Older Than Three Years

Batteries lose their ability to hold a charge over time and must be replaced periodically. 

Check the date stamped on your current battery and replace it if it’s more than three years old.

Fixed by Jump-starting

If you’ve ever tried jump-starting your car and it didn’t start on its own once you removed the jumper cables from the terminals, there’s a good chance your battery needs replacing soon.

Batteries that die suddenly often give you no warning signs beforehand; they won’t start at all one day.

The Engine Barely Turns Over

A weak battery can make starting your car difficult. If your vehicle takes three or four tries to turn over, there’s a problem with your battery.

The issue is caused by a weak or dead cell within your battery. A few more tries will eventually get things going, but it’s only a matter before your battery dies completely.

Horn Getting Weak

If your car horn has been sounding weak, your battery is about to die. Take this underdog sign rather seriously and replace your battery as soon as possible.

Without a working horn, you won’t be able to warn other drivers when they’re in danger or honk at them when they cut you off!

Battery Charge Warning Indication

If your car has an electronic display that shows how much charge is left in your battery, you may notice a warning light on the dashboard indicating that your battery is failing. 

If this happens, it’s best to take your car to a mechanic before heading out on your next trip.

The smell of Rotten Eggs

A bad battery gives off hydrogen sulfide gas which smells like rotten eggs. The sulfur in your battery is supposed to be released as it works, but if you smell rotten eggs or any other strange odor coming from under the hood, it could mean that the sulfur has built up and needs to be cleaned out.

Distorted Battery Casing

A distorted battery casing indicates that the casing has been exposed to high temperatures for a long time, which causes it to warp or melt. This may have happened if the battery was left on charge for too long or if it was left in direct sunlight.

When this happens, the acid inside the battery will spill out through weak spots and corrode the casing. If you see any distortion in your car battery, it’s time to replace it before it becomes a safety hazard.

Lights are Dimm

A low-voltage lightbulb indicates that the electrical current isn’t strong enough to power the bulb. If this happens often, it could signify that your battery is dying or dead already.

Battery Corrosion

A corroded battery can be dangerous because it may leak corrosive acid into your engine compartment, damaging other parts of the car and even starting a fire!

To avoid this, check for corrosion around the terminals and under caps periodically to ensure they’re clean and free from corrosion-inducing dirt or grime that could damage them over time.

How Does an Alternator Work?

An alternator is a device that converts mechanical energy into electrical energy. It is a generator that uses the engine’s rotation to produce electricity. The generated electricity is then used to charge the battery and power other electrical components in the vehicle.

They’re usually mounted on the front of the engine and have three main components: a drive belt, a rotor, and an alternator stator.

The drive belt connects to the crankshaft pulley on one end and an idler pulley on the other. The rotor is connected to this idler pulley via a set of bearings. Inside the alternator’s body is copper windings attached to a stationary housing (the stator).

Turning your car’s ignition key generates electricity that passes through these coils, producing a current of 12 volts or more depending on your engine size and model year. This current flows back through the drive belt into your car’s electrical system.

The main purpose of an alternator is to keep the battery fully charged while you drive. The alternator works with your battery and starter motor to provide power for all your electrical needs during normal operation.

Check Out Bad Alternator or Bad Battery, Easy Solved:

Signs of a Faulty Alternator

The alternator is a crucial part of your engine as it produces the electrical power to power all of your vehicle’s accessories. If you have a dead battery or an engine that won’t start, it could be because of a faulty alternator.

Here are some signs of a bad, faulty alternator:

Dashboard Warning Light Is On

A dashboard warning light or lamp indicates that your alternator has trouble generating electricity. The most common indicator lamp is usually found on the instrument panel, which is easy to see.

The battery will also appear on the gauge and should be fully charged when the car is running. If it isn’t, you’ll need to get the alternator repaired right away.

Unusual sounds

An alternator makes a lot of noise when it works. This noise can be loud or soft, depending on how well the alternator works. If you hear a strange sound coming from your car’s engine while running, it may indicate something wrong with your car’s electrical system.

The sound could be coming from your alternator or power steering pump. You should immediately get a professional mechanic to ensure everything is okay with your vehicle’s electrical system and there are no other problems.

Electrical issues

Ideally, your vehicle’s electrical system should be in top-notch condition. Otherwise, you will start experiencing problems with other parts of your vehicle, like lights and electronics.

Your headlights may dim unexpectedly without warning or completely fail after being turned on for about 20 seconds. You might also experience problems starting up; this may be caused by faulty alternator or belt tensioner issues that prevent proper belt tensioning and thus cause poor battery charging capabilities.


If your battery is not getting charged properly, it will run down quickly. You can check if this is happening by using a voltmeter to measure how much voltage is being produced by your car’s charging system.

If it is lower than 13 volts, you have an undercharging problem. This could be caused by a faulty alternator or wiring issue with your car’s charging system.


An overcharging alternator can severely damage your car’s battery, causing it to overheat and fail prematurely.

 If you notice that your battery is hot and swollen, or if it starts leaking fluid, you should have it checked immediately because this could be a sign that your alternator is overcharging.

The engine stalls

An alternator provides electrical current for vehicle systems like ignition and charging while you’re driving.

If there is no charge from your alternator, then these systems won’t function normally and won’t be able to start the car when needed.

Burning smell

A burning smell is often associated with an engine fire, but it can also indicate that something isn’t quite right with your alternator.

Don’t ignore it if you start smelling something burning under the hood! Get it checked out as soon as possible by a professional mechanic.

Flickering Lights

If you notice flickering headlights when you turn on your vehicle, this could indicate a bad alternator. If you notice this issue, make sure to have it inspected by a professional immediately.

The longer you wait to have it repaired, the more likely you’ll experience other issues with your car’s electrical system.

Dead battery

A dead battery is one of the most common signs of a bad alternator — especially if it’s dead for no apparent reason and doesn’t turn over when you try to start your car. 

How to Troubleshoot an Alternator Problem

If you’re having trouble with your car’s alternator, there are a few things you can do to troubleshoot the problem.

  • First, check the battery. Is it fully charged? If not, recharge it. If that doesn’t work, replace the battery.
  • Next, check for loose or corroded connections on the battery terminals.
  • If none works, check the voltage regulator (if your vehicle has one) and make sure it’s working properly.
  • If all else fails, take your vehicle to a professional mechanic who can diagnose what’s wrong and fix it for you!

Check Out How to Test and Troubleshoot an Alternator Problem:


How Do I Know if It’s My Battery or My Alternator?

The battery and alternator are often confused. 

If you have a bad battery, it’s usually fairly easy to diagnose: check the voltage at the battery terminals with a voltmeter. If it’s low, you’ve got a problem with your battery or charging system.

If it’s above 13 volts but not enough to start your engine, it’s probably related to your charging system (alternator).

How Can I Test if My Alternator Is Working?

A bad alternator is one of the most common causes of car battery failure. It’s a simple test to determine if it’s working properly.

Ensure your engine is cold, turn off all accessories and lights, and disconnect the battery. Start the engine and let it idle for a few minutes to ensure that all electrical components receive power.

You have a good alternator if your voltage gauge reads between 13-14 volts with no lights or accessories on. You may need to replace it if it reads lower than 12 volts.

How Much Do Alternators Usually Cost?

Alternators are one of the most important parts of a vehicle’s electrical system, but they can be expensive to replace. The average price of an alternator ranges from $200 to $500, depending on the make and model of your car.

How Do You Start a Car With a Bad Alternator?

You can start a car with a bad alternator by using jumper cables. First, connect one cable end to the positive terminal on your battery.
Then, connect the other end of the cable to a good battery in another vehicle. This will provide enough power to get your car started and running again.

What Happens When the Alternator Goes?

When the alternator goes, you can expect to lose power. The alternator is responsible for regulating voltage, so when it goes out, your battery will start to drain at a faster rate than usual.

This can lead to insufficient power in your vehicle’s electrical system, which could cause lights or other electrical components to fail.

Final Considerations

Identifying the difference between a bad car battery and a bad alternator is difficult. While several signs can help, you’ll need to consult your vehicle’s manual for complete instructions and details. 

Use this guide as an introduction, but understand that professionals can help you in case of a serious problem. If you’re not comfortable with battery and electrical issues, seek out a professional who is.

Agustin is part of the team at Road Speed Solutions, a reliable and efficient roadside assistance business with over a decade of experience in New Jersey.

What sets Road Speed Solution apart is the team's commitment to giving back to the community, regularly donating to local charities and supporting small businesses. Choose Roadside Speed Solutions for prompt, trustworthy roadside assistance services.