Will Dead Battery Hurt Alternator? – BatteryFever (2023)

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The function of an alternator in a car is to engineer the conversion of the mechanical energy of the car engine into electrical energy that recharges the car battery when the engine is running.

Does this however mean that the alternator can be used to recharge a car battery that is completely dead or will it get hurt while trying to do so?

So, will the dead battery hurt the alternator? The primary design of an alternator is not in recharging a dead car battery, rather, it is used to recharge the battery charge while the car is running.

There are various electrical components or gadgets in a car that continuously drains out the battery charge, the job of the alternator, therefore, is to keep on recharging the battery while the car is running.

To recharge a dead battery, it will take an alternator working at its highest capacity, that is, at 100% capacity to do so.

However, alternators are not engineered to be able to withstand working at such capacity for an extended period.

This explains that using an alternator to recharge a dead car battery hurts the alternator and may cause its untimely failure.

So, if an alternator should not be used to recharge a dead car battery, how can a dead car battery be revived?

The safest way to do this will be to take the battery to the car repair shop with the facility of recharging the dead battery. This should be done before connecting the car battery to the alternator.

(Video) Can A Dead Battery Ruin Your Car's Alternator?

Table Of Contents

  • 1 Why does a dead battery hurt the alternator?
  • 2 Can a dead battery damage the car alternator?
  • 3 Does driving with a dead battery suffice to charge it?
  • 4 Will Dead Battery Hurt Alternator – Conclusion

Why does a dead battery hurt the alternator?

To understand why this, happens and why you should not attempt to use the alternator with a dead battery, you have to first understand the working mechanism of an alternator and the physics behind how it recharges the car battery.

This way, you will be able to understand why recharging a dead car battery with the alternator is beyond the alternator’s engineering and will get it hurt.

Alternators generate the electrical current that recharges the car battery while the engine is running, but how does it do this? a flashback at elementary physics shows that electrical current can be generated from a magnetic field and a magnetic field can be created from channeling current through a wire coil.

The amount of electricity generated by a coil of wire is proportionate to the magnitude of the magnetic field and vice versa.

This principle is central to the working mechanism of the car alternator. The device is composed primarily of b basic parts; a rotor which spins to create the magnetic field, the voltage regulator which works synergistically with the rotor by sending current to the rotor to be used in creating the magnetic field.

The stator is the part of the alternator which is excited by the magnetic field generated by the rotor to produce an alternating current.

The last component of the alternator is the bridge rectifier, this will finally convert the alternating current generated by the stator into a direct current.

These parts are engineered to work together to generate the current needed to refill the charge in a car battery as the engine runs.

(Video) Bad Battery Or Bad Alternator? - How To Tell The Difference

They also work together to generate the electricity that is sent to other parts of the car such as the headlights.

The amount of alternating current generated by the alternator rotor depends on the load placed on the electrical system.

Whenever there is an additional load, this is sensed automatically by the voltage regular which controls the amount of alternating current the rotor generates.

Let’s say the car headlights are turned on, this is sensed by the system as an increased load which then triggers increased generation of alternating current by the rotor which is then converted by the stator into a direct current which the car can make use of.

So, each time there is an increased load, the voltage regulator senses this and alerts the rotor to increase the amount of current generated and vice versa.

So, why is recharging a dead battery with an alternator something that hurts the alternator? This is because the current requirement of a dead battery is beyond what the alternator can cope with. When a battery runs down, in that state, the car battery can be compared to a vampire thirsty for blood.

A huge amount of current is required to get the battery back on its feet, the alternator is simply not designed for such resurrection, and pulling such stunt with it will simply get it damaged.

To continue to work effectively, the alternator rotates between a state of rest and active current generation, without much rest, the device wears down and may begin to fail.

Saddling the device with such a huge responsibility of recharging a dead battery creates a continuous work cycle without any period of cooling for the alternator which contributes to its eventual breakdown.

A dead battery is therefore one of the primary causes of alternator failure as it forces the alternator to work at its full capacity without cooling for an extended period. Without getting cooled, the alternator is bound to overheat which gets it damaged.

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Can a dead battery damage the car alternator?

It is a common occurrence to find the car battery completely drained out after overnight parking or after leaving the car parked for several days.

This is commonly due to mistakenly forgetting to put off the indoor lights or other power consumers during this period or as a result of another parasitic battery drain.

A car battery is only required to get the car started; the alternator takes over immediately after. So, if one can get the car started, can the alternator work to get the dead battery recharged without sustaining any form of damage?

There are reports from those who have attempted to pull this stunt and discovered the battery did not get charged with the drive.

Their car mechanics are undecided regarding the cause for a damaged alternator. How true is the claim that an alternator can get damaged this way?

A good number of car owners claim to have used the car’s alternator to recharge a dead car battery back to life without causing any form of damage to their alternator.

A weak battery should however go through deep charging before getting connected to the alternator.

If the alternator fails to charge the dead battery back to life, does this automatically mean the alternator has become damaged? This may not be the case.

There are other reasons or explanations for an alternator failing to charge the car battery, this could be as a result of the battery being dry or damaged.

(Video) How to Test an Alternator

The only way out for a damaged battery is to get it replaced. It may also be a result of a wiring problem. The wiring connecting the alternator and the battery should be checked for faults, breakages, or loose connections.

Does driving with a dead battery suffice to charge it?

Many car owners and drivers have this belief, that is, by driving the car about, the alternator can charge the dead or flat battery back to full capacity forgetting that this is not the engineering goal of the alternator.

Deep charging a dead battery that has run out of charge completely is a huge responsibility requiring an enormous amount of current which is beyond what the alternator can generate consistently without getting hurt.

Maintaining the battery’s charge while the car runs is what the alternator is originally designed for and not battery resurrection.

The components of the alternator at the most risk of damage when the alternator is placed in such a precarious position are the alternator’s voltage regular and the rectifier.

Car mechanics have recorded numerous cases of the car’s alternator failing as a result of the car owner or driver attempting to make use of the alternator to recharge back to live a dead car battery.

Whenever you have a dead battery, the appropriate thing to do is to get it out of the car, and ensure its water level is adequate, that is, the battery is not dry. Then plug the battery into a wall charger to get it charged.

There are instances where driving with a dead battery caused no harm to the alternator, indicating that this is not a consistent occurrence.

Therefore, the car can be driven with a dead battery if there is no time to get the battery charged first, such as in an emergency.

Do not be in haste to conclude on alternator failure without running a proper diagnostic test on the alternator. If the voltage output of the alternator is within the normal range, that is, 13.8 to 14.4 volts, then it can be said still be viable.

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Will Dead Battery Hurt Alternator – Conclusion

The car alternator generates the current that keeps the car battery charged, it is however for maintaining the battery charge and not for recharging a dead battery.

While driving with a dead battery and expecting the alternator to get it charged back to life may not always hurt the alternator, it is one of the possible causes of alternator failure.


Will a dead battery ruin 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.

Can a bad battery cause electric power steering problems? ›

The power steering is an electrical system, so a problem with the battery could affect the power assistance. You should still be able to steer the car even without power assistance.

Can you jump a car with dead battery & bad alternator? ›

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. However, the alternator should be replaced as soon as possible.

Can a bad battery cause low charging voltage? ›

Bad Cell Lowers Charging Voltage

Because normal charging voltage can't be achieved on a battery with a bad cell, the alternator will overcharge the remaining cells and boil the electrolyte.

What can ruin an 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.
Jul 26, 2021

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

Generally, it usually takes between 30 minutes and an hour for an alternator to fully charge a battery if you are driving. If you want to charge your battery idle (when the engine is running but you're not driving), then it's going to take longer.

What problems can a dying car battery cause? ›

Can a Bad Battery Cause Electrical Problems? Yes, if your battery is underperforming it can cause systems within the vehicle to malfunction. A bad battery can also result in air conditioners, stereos and other applications not receiving enough power to function properly.

What damage can a bad car battery cause? ›

Internal components: A weak battery affects performance by causing damage to the engine's internal parts. The low voltage causes the temperature to go up, and overheating can result, which causes damage to the engine parts.

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

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.

What happens if alternator fails while driving? ›

What happens when alternator stops working while driving? The car tends to slowly lose power if the alternator has gone bad while the car is being driven. You'll notice the headlights start to dim shortly before the car loses power and dies.

Can you damage your alternator by jump starting? ›

Blown Engine Control Unit (ECU)

A blown ECU can occur if there is a voltage spike when jumpstarting. This impacts the alternator and other electrical components such as the fuel pump, onboard computer and possibly the fuses.

Will a new battery start a car with a bad alternator? ›

If the battery is dead replacing the alternator will not make the car start. And the car needs to be running and the battery fully charged in order to test the alternator. don't recommend trying to jump start the car.

Why is my alternator not putting out enough voltage? ›

Charging problems can be caused by electrical faults in the alternator or voltage regulator, poor wiring connections at the battery or alternator, or a slipping or broken drive belt. Since most late-model import alternators are internally regulated, a failure of the regulator means the alternator must also be replaced.

Will battery voltage drop if alternator is bad? ›

If your alternator is starting to go bad, its ability to maintain the battery's charge will falter, and all those electrical components will start to drain the battery.

What should battery voltage be with alternator? ›

A good alternator should maintain battery voltage between 13.9 and 14.8 volts (14.2 is optimum).

How much does it cost to get alternator replaced? ›

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 does it feel like when your alternator goes out? ›

Dim or Overly Bright Lights

Generally, that takes the form of under- or over-performing equipment, such as headlights that are either too dim or extremely bright. You may also experience flickering lights or lights that erratically go from bright to dim and vice-versa.

How long should 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.

Can a completely dead battery be recharged? ›

It is possible to recharge a dead battery, and depending upon the situation you are in, a dead battery is generally an easy fix, whether you are stuck in your garage and can handle it yourself or you are in the middle of nowhere and need professional, quick, and efficient service in the blink of an eye.

Will alternator charge battery while idling? ›

Do Car Batteries Charge While Idling? A car with an idling engine will still recharge your battery, but at a much lower rate than if you were driving. The reason for this is that modern cars have a lot of additional electronics that use up power.

Will a car battery recharge itself overnight? ›

Simply put, no car battery, whether healthy or dead, can charge itself. It always requires an external power source to get charged. Can Dead Batteries be Charged? Once a car battery is dead, the alternator will fail to recharge it completely.

What happens when a car battery fully dies? ›

First, your vehicle's engine will die immediately. You may notice it sputtering out as the alternator dies. After the alternator stops and the battery depletes, the engine goes off.

What happens if your car battery is completely dead? ›

"If your car does not start after a jump, your battery is likely completely dead and will need to be replaced. Your choices are to call for a towing service to bring your car to a repair shop or your residence, or roadside assistance, which may make their own attempt at jump-starting.

Can an alternator drain a battery overnight? ›

In some cases, it can be severe enough to deplete your fully charged battery overnight. Although you can test any circuit for a parasitic draw, this is how it works for a draw on an alternator, and all you need is a digital multimeter. Fully charge the battery.

How long will a car run with a dead alternator? ›

Since the alternator is a vital part of the battery's power system, you're going to need a repair as soon as possible. You can usually drive 25 to 30 minutes as long as your vehicle's battery is fully charged.

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 battery be too dead to jump? ›

Can a car battery be “too dead” to jump-start? No, a car battery is never “too dead” to jump-start. If the jump-start doesn't work, you may have a faulty alternator or a dead battery that necessitates a replacement.

Will a bad alternator throw a code? ›

If you have a “Check Engine" light on, connect a code reader to the diagnostic port. 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.

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

An alternator that is failing doesn't meet your car's electrical needs. This could cause your headlights to flicker or go from dim to bright. The alternator is not generating enough power to keep the lights on consistently. It will also affect your dashboard lights, and in some instances, they will even stop working.

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.

How long do you have to leave jumper cables on before starting? ›

Allow both vehicles to run connected for about three minutes. Leave the jump-started vehicle running and disconnect the cables in the reverse order that they were attached and close the hoods. Keep the jump-started vehicle's engine running for about a half hour to allow the battery to fully charge.

Why you shouldn't jump start a car? ›

A damaged battery has the potential to start a fire when placing the jumper cables on. Car batteries contain sulfuric acid that can become vapors, leaking out of vents. These vapors can be highly flammable. Jumper cables are known to cause sparks and can ignite these vapors, causing fires or even possibly an explosion.

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 I drive with a low voltage 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.

How do I know if my alternator fuse is blown? ›

The charging system warning light on the dashboard will likely illuminate if the alternator fuse is blown. A blown alternator fuse can also trigger the check engine light and many other dashboard warnings due to system undercharging.

Can a bad alternator destroy a car battery? ›

A faulty alternator could ruin a perfectly healthy battery, which would put you further back from a solution than where you started. Don't fret as diagnosing your vehicle's electrical problem is so easy that anyone can do it by running these tests.

At what battery voltage will a car not start? ›

When the voltage of the starting power supply is lower than 11.8V, it will be difficult to start the car. You can choose to turn off all other electrical appliances and try several times. When the battery voltage is lower than 10.8V, it is generally impossible to start the car.

What voltage is too low for a car battery? ›

12.0 volts or below - At 12.0 volts your battery is considered to be fully discharged or 'flat' and should be recharged as soon as possible. The lifespan of your battery will be severely affected if it remains within this voltage range for extended periods of time.

Why is my alternator only putting out 13 volts? ›

For some alternators, it's normal to see as low as 13 volts. For some, a constant 13.6 volts is an indication of a problem. For others, it's normal to see as high as 16 volts for long stretches. Still, it's perfectly normal for others to see the alternator not charge at all intermittently.

Does jump starting a car damage the alternator? ›

Impact on alternators from jump starts: The alternator's design makes it fairly impervious to negative effects from jump starting. However, the alternator can sustain instant damage if the polarity of the clamp connections is mistakenly reversed.

Will an alternator work without a battery? ›

Yes it can but you will burn up the alternator as the system uses the battery to help control the voltage regulator as many cars need a reference voltage.

How long will a full battery last without an alternator? ›

Most car batteries that are in good condition will last at least two weeks without needing you to start the car and drive to recharge it. But if you don't intend to drive your car for some time for whatever reason, you should still start it up once a week to recharge the 12-volt battery.

How far can you drive with a new battery and dead alternator? ›

Since you're wondering how long you can drive with a bad alternator, your car is likely having other issues. Since the alternator is a vital part of the battery's power system, you're going to need a repair as soon as possible. You can usually drive 25 to 30 minutes as long as your vehicle's battery is fully charged.

How does a car act when the alternator is going out? ›

Signs of a Bad Alternator

Some of the things to look for are no-starting and trouble starting, dimming lights and problems with stereo system output. If your car starts but stalls when you're underway, your battery is probably not being recharged due to a faulty alternator.

What happens if you don't replace alternator? ›

If your alternator isn't working as it should, it won't be able to charge up the battery. This means that the battery power levels will slowly decrease, and the battery will eventually die, leaving your car completely unresponsive.

What should alternator voltage be with bad battery? ›

Tip: If the battery is low you may want to have it load tested. Read the voltage on the meter - Start the engine and observe the voltage on the meter. The voltage should read a minimum of 13 volts. A good alternator should put out between **13.5-14.5 volts.

Will idling a car charge the battery? ›

Do Car Batteries Charge While Idling? A car with an idling engine will still recharge your battery, but at a much lower rate than if you were driving. The reason for this is that modern cars have a lot of additional electronics that use up power.

How long do you have to wait to run a car after replacing the alternator? ›

Ideally, you should drive the car around for 30 minutes to allow the alternator to charge the battery to a good level. Even after that if you still have a flat battery, it could be an issue with the alternator.

Can you replace an alternator in a day? ›

So how long does it take to replace an alternator? This is a common question with an easy answer. The make and model of your vehicle will determine the exact time it takes to replace the alternator, but usually, one to two hours is sufficient.

How long will a car drive with a bad alternator? ›

Since the alternator is a vital part of the battery's power system, you're going to need a repair as soon as possible. You can usually drive 25 to 30 minutes as long as your vehicle's battery is fully charged.

Can a new alternator drain an old battery? ›

Contrary to its purpose, an alternator can drain a battery. It's rare, but it's possible. A draw on the battery only occurs if there's a problem with either a component in the alternator itself or connections to it.


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