Signs of Bad Car Battery vs Alternator (Causes and Solutions) (2023)

It can be very frustrating and inconvenient when your vehicle won't start. But what causes this problem?

Well, there are many reasons why your car won't start. But perhaps the most common causes are problems with the battery or the alternator.

Most people don't think much of their car's battery and alternator until the engine dies while driving or the car doesn't start normally.

But honestly, it's hard to tell if it's a dead battery or a bad alternator if you don't know how these electrical components work.

In this guide, we take a look at how a car's battery and alternator work. We've also highlighted the telltale signs and symptoms of a bad battery and alternator to help you troubleshoot your car.

How do the battery and alternator work?

Signs of Bad Car Battery vs Alternator (Causes and Solutions) (1)

Car battery

Your car's battery is an integral part of a finely tuned electrical system that keeps the vehicle's processes running smoothly. It stores the energy the car needs to start the engine and maintain the charge.

Car batteries have different voltage levels, with 12 volts being the most common. A slight drop in voltage levels may result in reduced performance. Therefore, you must ensure that the battery charge is adequate at all times.

If the voltage drops above 10.5 volts, your battery will be damaged by excessive sulfation. Fortunately, there are a few things you can avoid discharging the batteryand the depletion of their energy reserves.

The battery not only serves to store the vehicle's energy, but also provides enough electrical energy to run the engine. It also serves as a reliable backup power source to power your car's electrical accessories when the alternator overloads. This happens when several processes, depending on the power of the generator, are running at the same time.

Additionally, the battery provides the energy needed to power electrical components such as a dash cam or lights when the vehicle is not running.

(Video) Bad Alternator or Bad Battery, Easy Solved

Before we forget, the battery helps regulate voltage. Regulates current going to electrical systems, preventing sudden voltage spikes that can damage the vehicle's computer and ignition system.

Because car batteries have to withstand all of these voltages, they are designed to immediately discharge and recharge many currents. However, if you repeatedly turn on the battery without fully charging it, it will lose its ability to hold a full charge. As a result, battery problems may arise.


Signs of Bad Car Battery vs Alternator (Causes and Solutions) (2)

Think of the alternator as a small generator that keeps your car's air conditioning, lights, sound system, and all the other accessories running. As the name suggests, this device is powered by alternating current (DC) and converts mechanical energy into electrical energy.

The alternator also actively charges the battery when you are driving your car. The alternator produces a voltage between 13 and 14.5 volts. However, the amount of current generated varies from vehicle to vehicle.

Equipped with a stator, rotor, diode, and fan, an alternator is always running when your vehicle accelerates. This allows you to supply power to the entire car.

But when your car is stopped, such as at a red light or stuck in traffic, the alternator doesn't work at full power. Instead, it generates enough power to run the engine and run major accessories like HVAC, water pumps, and cooling fans. Also, the battery will not be fully charged.

Reasons why a battery or alternator can fail

Most people believe that battery or alternator failures are due to manufacturer error. While this is not far from the truth, there are other reasons for failure. They include:

1. Driving habits

Sometimes your driving habits can contribute to your car battery draining. It does not mean that you are a bad driver. It's more about the chemical process in the battery.

When the car is idling, e.g. B. in heavy traffic, it can discharge the battery, leading to sulfation. When this happens, the battery takes longer to charge, loses power quickly, and eventually runs out.

To reverse sulfation, it is recommended to travel longer distances to ensure that the battery is fully charged. Another solution is to purchase an anti-sulfation device that allows you to apply pulses to the battery terminals.

(Video) Bad battery or bad alternator symptoms, how to tell the difference (brief) not charging. - VOTD

2. End of alternator life

Alternators typically have a useful life of 6 to 10 years or 80,000 to 150,000 miles. Also, they may not work optimally.

An old or faulty alternator will have trouble charging the battery with the engine running, causing it to drain faster than normal. This can result in a dead or discharged battery.

Hot weather or higher temperatures can also shorten the life of an alternator.

3. Cold weather

Just like with alternators.Temperature plays a crucial rolewhen determining the performance and life of a battery.

High temperatures speed up chemical reactions within the battery, allowing it to charge faster. However, temperatures can accelerate battery corrosion, which in turn shortens battery life.

Cold temperatures, on the other hand, slow down chemical activity. Because of this, the battery can perform slowly in cold weather, even when fully charged. The cold temperatures reduced the battery's capacity to provide enough power to start and operate a vehicle.

A fully charged car battery can withstand temperatures down to -50°C. But a weakly charged battery can freeze at -1°C. When battery water freezes, it expands and causes irreparable damage to the electrochemical cells.

4. Non-computer problem

Signs of Bad Car Battery vs Alternator (Causes and Solutions) (3)

Newer car models are equipped with on-board computer systems that control a variety of components, including alternators. If these systems develop a problem or malfunction, they can prevent the alternator from providing power to the engine and charging the battery.

5. Defective fuse

blown fusesit can prevent the alternator from working and the battery will not be charged. So if you have a bad or faulty alternator, read your owner's manual to determine where the fuse is located in the car. Once you locate the fuse, check to see if it has blown.

Signs and symptoms of a bad car battery

1. Slow crank

If a vehicle takes longer to start, it is likely due to low battery voltage or a dead battery. This can happen if you leave your car's ignition and interior lights on overnight. If the battery discharges completely, you risk damaging the cells.

(Video) Symptoms, Causes Of Alternator Overcharging, And How To Fix It

2. Darkened or no headlights

Flashing or dim headlights indicate that the battery is low. When the headlights don't turn onYou probably have a dead car battery.or a faulty electrical system.

3. Clicking noises

If you hear unusual clicking noises when you start your car, it is likely that your battery is dead. The battery is not supplying power correctly.

4. Battery corrosion

Corrosion on battery terminals often prevents cells from charging properly. As a result, the battery cannot store enough charge to start the vehicle. In this case, it may be necessary to remove the corrosion and skip the battery. If the engine won't start, you have a bad or dead battery.

5. Strange smell

The smell of rotten eggsit is a clear sign of a faulty car battery. This strange smell means that the lead-acid battery is leaking sulfuric gases. Therefore, you should get a new battery immediately.

6. Engine barely starts

The battery does not have enough power to start the engine. Here you can use jumper cables to connect the battery.

Signs and symptoms of a bad alternator?

1. Smell of burning

A bad smell of burning or spinning rubber could mean that the alternator belt is worn from constant friction. It's also a sign of an overloaded alternator or frayed or damaged wires.

2. Weak or very bright light

Another way to tell if you have a bad or failing alternator is to look for above-average or below-average electronics. For example, you may notice flickering lights or lights that suddenly become bright.

3. Dashboard warning lights

If the battery icon lights up on the panel, it means a charging system failure. But if the car's lights and electrical components continue to function normally, you have a faulty alternator.

4. Battery discharged

If you've just installed a new battery and it suddenly dies, it could mean your alternator is bad. Does not charge the battery.

5. Accessories malfunction

When an alternator doesn't produce enough power to drive the vehicle's electronic components, it can malfunction. A faulty alternator will not light the windows. And when you increase them, they take longer to rise or fall. Other accessories can also go wrong.

(Video) Dead Car Battery or Low Voltage Warnings? Diagnose Battery and Alternator

What to do with a faulty battery or alternator?

If you see the warning signs above, it's best to replace the battery or alternator. However, before you think about replacing or repairing the battery, check whether the battery has any problems.

Paso 1:Check if the battery level indicator is flashing

Paso 2:Use a voltmeter to determine if the battery voltage is less than 12.6

Stage 3:Make sure commonly used connections like power windows are working properly

as soon as you confirmthe battery is the problemReplace it yourself or contact a mechanic.

Check the alternator to see if it is the source of the problem by disconnecting the positive battery cable while the vehicle is running. If your car stops running, your alternator is faulty.

Replace the old alternator with a new one. However, since alternators are expensive, you can buy a used one to save some money.


In conclusion, a bad alternator and battery can cause your car's engine not to start or your car to stop abruptly. However, you can use this information to quickly find and fix the problem.

Hopefully you now understand how these auto parts work and the signs and symptoms to recognize a bad battery and bad alternator.

If you feel we have missed some details or have any questions, please let us know in the comments section.


(Video) Bad Ground Connection On Cars-Meaning,Symptoms, Diagnosing and Solving The Problem

Related Posts:


How do you tell if it's a dead battery or alternator problem? ›

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.

Can a bad battery act like a bad alternator? ›

A bad battery won't usually harm your starter or alternator, however, since both of those components get their voltage directly from the battery, if the battery is underperforming, both the alternator's and starter's performance will be affected as well.

Will a car start with a good battery and bad alternator? ›

If your alternator is dead, the car might start but will be running solely on the battery. Can you jumpstart a car with a bad alternator? It is possible in some cases to jumpstart a vehicle that has a faulty alternator, as long as the battery has enough of a charge to keep running.

How do I know if I need a new battery or a new alternator? ›

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.”

What happens when alternator goes out? ›

A bad alternator will result in a discharged (dead) battery and cause a vehicle to not start or run. Alternators are designed to maintain a battery's charge, not to recharge a dead battery. Your alternator's job is to maintain a consistent charge on your battery. Draining your car's battery is not advised.

What problems can a bad battery cause? ›

Here's a look at five strange problems common when a battery is on its way out and some pro tips to avoid battery-related headaches.
  • Random and Spontaneous Illumination of Multiple Warning Lights. ...
  • Ignition / Door Locks / Windows / Accessories with a Mind of Their Own. ...
  • Auto Start/Stop Failure. ...
  • Spontaneous Alarm Activation.
Mar 25, 2020

What are the symptoms of a bad battery? ›

Watch for these five telltale signs of a bad battery so you aren't caught out in the cold!
  • Dim headlights. ...
  • Clicking sound when you turn the key. ...
  • Slow crank. ...
  • Needing to press on the gas pedal to start. ...
  • Backfiring.
Jan 7, 2018

Can a weak battery destroy an alternator? ›

A weak battery cannot have any effect on alternator, but a poor or weak alternator can deteriorate the battery very quickly. A broken battery also has an effect on an alternator as it puts more pressure and stress on the alternator while working and sometimes destroy the alternator as well.

Will a car stay running if the alternator is bad? ›

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.

Is it my car battery or alternator? ›

If your windshield wipers, brake lights, and automatic windows aren't working, then the battery is likely dead. If they are working, however, the problem likely lies with the alternator.

Will a bad alternator drain a battery when 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.

What is the most common problem with an alternator? ›

One of the most common problems you're likely to experience with an alternator is a failure in the bearings. There are needle bearings in the alternator that allow the rotor to freely spin inside the housing, and those bearings can break down over time as a result of exposure to heat and dirt.

What does a bad alternator sound like when starting? ›

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.

Can a blown fuse cause alternator problems? ›

Dead Battery

As was mentioned earlier, the alternator charges the battery while supplying the rest of the car with electricity. If the alternator's fuse or fusible link is blown, the alternator will not be able to charge the battery.

Should I fix my alternator or buy a new one? ›

You could save up to about half on a rebuilt alternator. In this process the broken parts are replaced, hence the term rebuilt. You may get up to a 90-day warranty. Remanufactured alternators still offer some savings, around 25% generally, and are different than rebuilt ones.

Can you fix an alternator instead of replacing it? ›

Alternators are simple machines & can certainly be repaired. You need to ask them exactly what part of that alternator has failed and that part can be replaced. For e.g. the alt may be mechanically sound but the brushes are worn out or the rectifier, regulator may have failed.

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!

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 is the average lifespan of a car alternator? ›

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.

How much is it to fix an alternator? ›

Alternators can average anywhere from $100 to $350, depending on the model. In most cases, costs will average between $350−400 for the alternator replacement if no other parts need to be changed. Add another $20 to $50 to your bill if the serpentine belt has to be replaced as well.

What are the three main causes of battery failure? ›

What causes battery failure?
  • The battery is not being used in the application for which it was designed.
  • The battery is not sized properly for the application.
  • The vehicle has excessive electrical accessories.
  • The battery is not properly fitted into the vehicle.
  • The battery cables are not clean.

What is the number one cause of battery failure? ›

Battery malfunction is seldom caused by a factory defect; driving habits are the more common culprits. Heavy accessory power when driving short distance prevents a periodic fully saturated charge that is so important for the longevity of a lead acid battery.

What is the main cause of battery failure? ›

Batteries are very susceptible to extreme temperatures. In hot temperatures, batteries will expel more energy than in a normal range of temperature. The heat causes a loss of electrolyte in the battery leading to an increase in discharge and eventual failure. The cold can be just a troublesome.

What destroys a car alternator? ›

There are several issues that can ruin an alternator: Using jumper cables wrong, Overloading the charging system with too many accessories, Leaking fluid, or. A tight belt that can damage bearings.

Will a new alternator charge a dead battery? ›

Does an Alternator Replace a Charger? An alternator cannot do everything a charger can. For starters, an alternator can charge a battery with a low charge, but it cannot charge a dead battery. As we said above, the battery's job is to start the engine and then work as an electrical load balancer.

Can AutoZone test your alternator? ›

Alternator Testing

Dim or flickering lights, dead battery, battery light on, trouble starting or other issues. How to get your alternator tested: Just to visit a nearby AutoZone. We'll test the alternator while it's still in the vehicle.

What is more important alternator or battery? ›

The Likely Culprit: Alternator

As important as the battery in your vehicle is, it really has one main job: to start the engine. If the alternator isn't working as it should, your battery won't have enough charge to start the engine, but that's not the only problem you may experience.

Why won't my car start with a new battery and alternator? ›

If you've replaced your battery but the engine still won't start, it could actually be an engine problem. A seized engine won't turn over, and that often resembles a bad starter or dead battery. If you suspect that your problem stems from an engine issue, it could take hours to diagnose and repair.

How long will a fully charged battery run a car with a bad alternator? ›

But how long can you drive with a broken alternator? We have researched this question and this is what we found. You should only drive 25 miles or around 30 minutes with a bad alternator if you have a fully charged and properly working battery. If your battery is low, you may need to be towed.

How do you start a car with a bad alternator? ›

How To Jumpstart A Car With A Bad Alternator
  1. Find Someone with a Good Battery. You can't jumpstart a dead battery without a fully-charged option at your fingertips. ...
  2. Let It Run. Before the jumpstart begins, you'll want to run the other engine for 3 to 4 minutes. ...
  3. Turn Accessories Off. ...
  4. Get Thee to a Mechanic. ...
  5. Use a Jumper Pack.

How long will a car run with a new battery and bad alternator? ›

Your engine will die in less than 45 minutes of driving.

Will a car start with a blown alternator fuse? ›

If the alternator's fuse or fusible link is blown, the alternator will not be able to charge the battery. The battery then doesn't store enough power for starting the car or keeping it running.

How do I know if it's my alternator or my starter? ›

Is It the Alternator, the Starter, or the Battery? Match Your Vehicle's Symptoms to the Most Likely Culprit
  • The Symptom: The Lights Dim & Flicker. The Likely Culprit: Alternator. ...
  • The Symptom: Dash Lights Turn On, But the Car Won't Start. The Likely Culprit: Starter. ...
  • The Symptom: Jump Start Doesn't Work.
Feb 25, 2020


1. Here's Why Your Car Battery Keeps Draining
(Everyman Driver)
2. Bad Alternator - Symptoms Explained | Signs of failing alternator in your car
(Auto Info Group)
3. Can A Dead Battery Ruin Your Car's Alternator?
(Engineering Explained)
4. How do I know if my Alternator or Starter is bad?
(Mercie J Auto Care, llc)
5. Diagnosing Alternator Problems - EricTheCarGuy
6. Bad alternator symptoms & How to tell


Top Articles
Latest Posts
Article information

Author: Chrissy Homenick

Last Updated: 07/23/2023

Views: 5954

Rating: 4.3 / 5 (74 voted)

Reviews: 81% of readers found this page helpful

Author information

Name: Chrissy Homenick

Birthday: 2001-10-22

Address: 611 Kuhn Oval, Feltonbury, NY 02783-3818

Phone: +96619177651654

Job: Mining Representative

Hobby: amateur radio, Sculling, Knife making, Gardening, Watching movies, Gunsmithing, Video gaming

Introduction: My name is Chrissy Homenick, I am a tender, funny, determined, tender, glorious, fancy, enthusiastic person who loves writing and wants to share my knowledge and understanding with you.