Signs Of A Bad/Dead Car Battery Vs Alternator: How To Tell? (2023)

Both the battery and alternator play essential roles in your car’s electrical system. And when one or both are not functioning correctly, it can cause a range of issues, especially not starting up or stalling.

The question is: which one is the culprit? Here are the different signs of a dead battery or alternator to identify the problem and get back on the road.

Table of Contents

How Car Battery And Alternator Work

Two of the most critical components in a car’s electrical system are the battery and alternator. Let’s see how they work!

Car Battery

The battery works by converting chemical energy into electrical energy through a series of chemical reactions. When the car is started, the battery sends a burst of electrical power to the starter motor, which turns the engine over.

As the engine runs, the alternator takes over and recharges the battery, keeping it in a charged state for the next start. The battery is also responsible for powering the car’s electrical components, such as lights and radio, when the engine is not running.


Signs Of A Bad/Dead Car Battery Vs Alternator: How To Tell? (1)

A car alternator is a device that generates electrical power to proper charge the battery and supply power to the electrical system while the engine is running. It works by converting mechanical energy from the engine into electrical energy.

The alternator produces an alternating current (AC) converted to direct current (DC) by a rectifier before being used by the car’s electrical system. The voltage output of the alternator is typically around 14 volts, which is used to charge the battery and run the car’s electronic components.

What Causes A Bad Car Battery Or Alternator?

The majority of people think that alternator or battery failure is the result of production flaws. This is true, but there are other factors at play as well, such as driving habits, extreme weather conditions, or loose wiring.

Driving Habits

Short trips and frequent starts can put additional strain on the battery, as it doesn’t have enough time to fully recharge. Similarly, long periods of inactivity can also cause the battery to lose its charge, leading to premature failure.

Aggressive driving habits, such as rapid acceleration and braking, can also put additional strain on the alternator, leading to premature wear and tear.

Extreme Weather

In hot temperatures, the heat can cause the battery to lose its charge more quickly, leading to premature failure. Meanwhile, extreme cold can also cause the battery’s electrolyte solution to freeze, damaging the battery’s cells and leading to permanent damage.

Harsh weather conditions can also lead to physical damage to the alternator, such as corrosion, water damage, or exposure to debris.

Loose Wiring

Signs Of A Bad/Dead Car Battery Vs Alternator: How To Tell? (2)

When wiring connections become loose, it can lead to poor electrical contact, which can cause voltage drops or spikes.

This can put additional strain on both the battery and alternator, potentially leading to premature failure. Loose wiring can also cause electrical shorts, which can damage the electric components of the vehicle.

Different Signs Of A Bad Alternator Vs Bad Battery

There are some obvious pointers of a faulty car battery and alternator, and understanding the difference between them can help you identify the issue and seek prompt repairs.

Signs Of A Bad Car Battery

Signs Of A Bad/Dead Car Battery Vs Alternator: How To Tell? (3)

Here are some common symptoms of a malfunctioning battery.

Slow Cranking

When a car struggles to start, the most common cause is a dead or low-voltage battery. If you leave the interior lights and ignition on in your automobile overnight, this may occur. You run the danger of causing the cells to break if the battery runs entirely dry.

Dim Headlights

Your car’s headlights require a significant amount of power to operate. If your battery is struggling to supply enough energy, you may notice that your headlights are dimmer than usual, especially when you’re idling.

When your headlights don’t turn on, your electrical system may malfunction, or your car battery is dead.

Electrical Issues

Faulty batteries can also cause various electrical issues in your car. For example, you may notice that your radio or air conditioning system is not working properly or that your power windows are slow to operate.

These problems can be caused by a weak battery that is not able to provide sufficient power to these systems.

Swollen/Bloated Battery Case

In some cases, a bad battery can also cause physical changes to the battery case. Whenever you notice that the battery case looks bloated or swollen, there is a good chance of a short circuit happening inside.

This is a serious battery issue that requires immediate attention, as it can trigger the battery to leak or even explode.

Odd Smell

When an auto battery starts to go bad, it can produce a sulfur or rotten egg smell. This is caused by the battery’s internal components breaking down and releasing hydrogen sulfide gas.

A burning smell is also quite common, resulting from a short circuit or an overloaded electrical system.

Signs Of A Bad Alternator

Signs Of A Bad/Dead Car Battery Vs Alternator: How To Tell? (4)

Below are the most common indicators of a faulty alternator.

Warning Light

An obvious signal of a bad alternator is when the battery warning light or check engine light comes on. This happens when the alternator is not generating enough power to charge the battery or when there is a problem with the alternator itself.

Flickering Lights

Once you notice that your headlights, dashboard lights, or other engine components are dimming or flickering, it could be a sign that your alternator is failing. This occurs because the alternator is not delivering enough energy to keep the electrical system running correctly.

Strange Noises

If you ever hear growling sounds coming from within your car, you may have alternator issues. The drive belt that rotates the alternator’s pulley might make a growling or whining noise if it becomes out of alignment or rubs against the pulley’s side. This sound may also be audible if the rotor shaft bearings are failing.

Dead Battery

A failing alternator can also cause the battery to lose its charge. If you notice that your automotive battery is weak or dead, even after a full charge, it could be a sign that your alternator is not working correctly.

Faulty Electrical Accessories

Frequently, slow or dysfunctional accessories are a sign that your alternator isn’t giving sufficient power to your car’s electronics. Your alternator may be faulty when you find that your windows are rolling up or down more slowly than usual.

Other symptoms include your seat warmers feeling odd and your speedometer or other devices start acting strangely.

Note: A faulty alternator will definitely destroy a battery, and it can’t be jump-started like the battery. So keep in mind these red flags to detect them soon so that you don’t end up replacing both the battery and the alternator.

How To Tell If Battery Or The Alternator Is Bad? Jumpstarting Test

The alternator or battery may be the cause of your car’s starting problems. Still, which one is the culprit? There is a relatively simple way to find out.

It’s crucial to understand how the automobile battery and alternator function together. When the engine is off, your car battery serves as the primary power source for a variety of tasks, including starting the vehicle.

When your engine is running, the car alternator assists in charging the battery. The efficient operation of your car depends on these two components, which work together to maintain the flow of power.

You might have a failed battery if your automobile won’t start at all. Suppose your vehicle temporarily begins and then stops abruptly, giving you a glimmer of hope that everything is alright; your alternator may be broken.

Take a jumper wire set and try to jumpstart your vehicle to determine if the problem is with the alternator or the dead battery.

Let’s say you can start the engine, but it shuts off quickly after. Then, your car’s alternator is probably incapable of recharging the battery. A dead battery, on the other hand, is most likely to blame if it struggles to start on its own but seems to recover when you jumpstart the automobile.

See more: Can A Car Battery Be Too Dead To Jump Start?

Frequently Asked Questions

Should I Continue Driving With A Bad Battery Or Alternator?

No, it is not recommended to continue driving with a bad battery or alternator because it can cause serious damage to your vehicle and potentially leave you stranded.

A bad battery can cause your car to stall or fail to start, and it can also cause damage to other components in your car’s electrical system, such as the alternator or starter.

Will A New Battery Start A Car With A Faulty Alternator?

No. Changing the battery won’t help the car start if your alternator is dead. Also, to test the alternator, the automobile must be operating, and its battery must be fully charged.

Can A Weak Battery Damage An Alternator?

Yes, a weak battery can damage an alternator. If the battery is weak, it may not be able to hold a charge or maintain the proper voltage level, which can cause the alternator to work harder than it should. Over time, this extra strain on the alternator can cause it to wear out or fail prematurely.

The Bottom Line

Understanding the warning signs of a bad battery vs alternator is crucial to keep your vehicle running smoothly and avoiding costly repairs. While the evident symptoms may sometimes overlap, there are specific indicators that can help you identify the problem.

Remember that a weak battery can revive by jump-starting, but a faulty alternator can only go to waste.


Signs Of A Bad/Dead Car Battery Vs Alternator: How To Tell? ›

Jumpstart your car. If you can turn the engine on, but it dies shortly thereafter, your car alternator likely isn't able to charge the battery. On the other hand, if you jumpstart the car and later on it fails to start on its own, it's likely a dead battery.

How do you tell if it's your alternator or battery? ›

“If the [battery's] voltage is low, replace with a new battery or charge the battery to the recommended 14.2 to 14.7 volts,” he says. “Then try to run the vehicle and see if the voltage after is outside of that range. If it is, that's a sign of a bad alternator.”

Can a bad battery be mistaken for a bad alternator? ›

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.

How do you check if your alternator is not working? ›

7 Signs of a Failing Alternator
  1. Dim or Overly Bright Lights. ...
  2. Dead Battery. ...
  3. Slow or Malfunctioning Accessories. ...
  4. Trouble Starting or Frequent Stalling. ...
  5. Growling or Whining Noises. ...
  6. Smell of Burning Rubber or Wires. ...
  7. Battery Warning Light on Dash.
Aug 24, 2020

Is it my battery or alternator or starter? ›

The Likely Culprit: Starter

If you're unable to start your vehicle, check and see if the headlights and dash lights come on. If they shine bright and clear, that means that the battery and alternator are likely not the cause of the problem. If they were, there wouldn't be enough power to run the lights.

Can AutoZone test an alternator? ›

Testing will ensure you identify a power issue correctly. How to get your alternator tested: Just visit a nearby AutoZone. We'll test the alternator while it's still in the vehicle.

Can a bad alternator drain a battery while the car is off? ›

A corroded or defective alternator diode will faultily continue charging the circuit even when the car off. This, in turn, will drain your car battery and cause the car not to start.

Will a car run with a bad alternator? ›

While you can technically still drive with a bad alternator, it is not advised. This is especially true in newer vehicle models. This is because there is more electricity involved compared to an older model.

Can an alternator be tested to see if it's good or bad? ›

The only way to know if an alternator is good or bad is to bench test it on an alternator test stand. Charging output can be tested on a vehicle with a digital voltmeter. A good alternator should produce about 13.5 to 14.5 volts with the engine idling.

Which battery cable do you take off to test the alternator? ›

You can check the alternator by simply starting your car and then disconnecting the negative battery cable. Be careful doing this, though, because there are a lot of moving parts in your engine compartment that could cause injury.

How does a bad alternator sound? ›

It requires a good deal of energy to crank the car's motor, and if a battery is not replenishing its power properly due to a faulty alternator, it will become drained and ineffective. You will hear a clicking noise while attempting to start the car, and the engine will have difficulty turning over.

What can drain a car battery when the car is off? ›

What may drain a car battery when it's off are things such as interior lights, door lights, or even bad relays. While your engine runs, the alternator recharges the battery — which is why you typically don't have to worry about the battery dying while you're blasting the radio on your drive to work!

Does dead battery or alternator click? ›

If you hear rapid clicking...

Perhaps your battery's dead, or your alternator, which charges the battery, isn't working correctly. If the source of the clicking is electrical, the starter (a small motor energized by the battery that gets the engine running) doesn't have enough juice to stay powered.

What happens when alternator goes out? ›

If a faulty alternator fails to keep your battery consistently charged, the fuel injectors may not fire, causing your engine to stall. A dying alternator can lead to a wide range of other electrical issues. Generally speaking, such issues manifest as an inability to perform at normal power.

What is the lifespan of an alternator? ›

How Long Does an Alternator Last? You may also be wondering about alternator lifespan. The average lifespan for most alternators ranges from 80,000 and 150,000 miles. Usually, an alternator lasts about seven years.

Why does my car struggle to start but the battery is fine? ›

If your car won't start but the battery is good, the most common cause is a faulty starter – though it could also be to do with your fuel. You may have insufficient fuel to get the car going.

Is it worth fixing the alternator? ›

Alternator issues won't go away on their own. They'll need to get fixed eventually, and if you wait too long, the issues might become more serious, leading to more expensive repairs and higher bills for you to pay. If you get the issue fixed early on, the repair will usually be much simpler and cheaper.

Will your car shut off while driving if the alternator is bad? ›

Alternator Issues

The alternator helps to manage the supply of electricity by recharging the battery. When there is a bad alternator, your car will shut off while driving. This primarily happens as it affects the power supply. Alternator issues will make the engine lose power.

Will a bad alternator throw a code? ›

If you find code P0562, you very likely have a failing alternator (note that codes may vary by vehicle make/model/year). Get it checked out before it fails entirely. If you suspect a failing alternator but don't have a warning light, pop the hood and check the condition of the belt.

Do alternators go out suddenly? ›

Alternators can go bad suddenly, or slowly over time. If your alternator is slowly going bad over time there are some warning signs you can look out for.

What spoils a car alternator? ›

Age and use-related wear is often the reason behind a dying alternator. Engine oil or power steering fluid leaking onto the car alternator can lead to its failure. Prolonged idling while using multiple electrical accessories can prematurely wear the alternator.

Can you disconnect battery while car is running to check alternator? ›

This is a common backyard mechanic technique to test if your alternator is working properly. In theory, if your alternator is providing adequate power to the car while charging the battery, then once the car is started, disconnecting the battery should not cause the engine to stop running.

How long does it take to charge a dead battery with an alternator? ›

Remember: After you've done a jump start, you'll need to keep the vehicle's engine running for around 30 minutes to allow the alternator time to charge the battery sufficiently.

How to tell the difference between a starter problem and a battery problem? ›

Lights on the dashboard that illuminate without a start show that the car has power, so it is likely to be a starter and not a battery problem. Finally, if you jumpstart a car but it still does not turn over, it is most likely the starter.

How do I know if my starter is draining my battery? ›

How To Know If Your Starter Is Draining The Battery
  1. Your Starter Makes Strange Noises.
  2. Lights Are on but Car Won't Start.
  3. Engine Won't Turn Over.
  4. Smoke or Strange Smell.
  5. Starter Is Soaked With Oil.

When I try to start my car it just clicks rapidly? ›

Usually a rapid clicking noise is a good indication that your starter motor isn't getting enough electrical current to engage – basically your solenoid is trying to engage but can't make the connection.


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