How Quickly Does An Alternator Charge A Battery? Guide (2023)

When charging your battery, the alternator should create a voltage slightly higher than just the battery voltage, causing current to flow into the battery until it reaches the higher voltage. However, do you know How Quickly Does An Alternator Charge A Battery?

Utilizing an alternator provides the advantage of faster battery charging. It takes 30 minutes to recharge the battery on the highway, but an hour or more in the city. If your alternator is in excellent condition, you should be able to charge a flat battery to around 80% capacity in about two hours.

The most significant charge that a fully charged 12 v battery charger may get is 14.2V. The alternator controls the rate at which the battery is charged. Many people assume that the car’s battery is in charge of the vehicle’s whole electrical system.

On the other hand, the alternator is in charge of ensuring that everything works properly. Rather than that, a tiny number of us may be concerned with the question, How Quickly Does An Alternator Charge A Battery? This page will give you all the necessary information on the time of the alternator charging a battery.

How Quickly Does An Alternator Charge A Battery? Guide (1)

What Is An Alternator?

The alternator is a term that refers to a device that generates electricity. The alternator’s function is to give electricity to the vehicle and recharge the battery. Except for a few hybrids and internal combustion engines, no automobile on the road today does not have an alternator.

It is customary to locate the alternator near the front engine and surround it with a strap. The most often asked question is if a malfunctioning alternator may deteriorate the battery. Naturally, when a battery cell is faulty, it may overcharge. Thus, familiarity with the specifics of an alternator is critical.

Alternator Components

The components of an alternator are intended to provide the vehicle with the necessary power. The following are the primary components and their functions in your car’s charging system:

Rotor And Stator

The rotor and stator are drawn together by an internal magnetic field, which spins the rotor around and around in the stator’s copper wire. Electricity is generated by the movement of magnets along a wire.


Rectifying Diode

Diode rectifiers convert alternator voltage to a form compatible with battery charge.

Regulator Of Voltage

The voltage regulator is in charge of maintaining the alternator’s output voltage. It monitors the battery’s voltage and distributes power to the vehicle’s remaining components.

Cooling Fan

Cooling the heat produced by alternators is required. They also include spinning fans for additional cooling in addition to the vents and metal casing. The fan blades in earlier versions are often located on the outside.

The Alternator’s Function

While the alternator is a critical component of your car’s power system, it’s worth noting that batteries fail much more commonly than alternators. The essential function of an alternator is as follows:

Electricity Is Generated

The voltage of a car’s battery varies depending on the engine’s condition. Before learning how the alternator generates power, it’s critical to understand how many volts a vehicle battery contains (car battery voltage chart). A combustion engine causes electricity. A serpentine belt drives the alternator in most current automobiles, and the belt’s movement supplies mechanical energy to the alternator’s rotor.

As the rotor revolves, it creates power. When the rotor’s magnets pass over the stator’s copper wires, they generate a magnetic field. In a stator, this magnetic field generates and stores electricity. The voltage regulator then distributes and regulates the battery’s voltage.

Battery Charge

Before the battery can use the alternator’s output, it must change the format. It is because electricity may travel in any direction. Alternators create alternating current (AC) power, which may flow in the opposite direction of the current provided by a vehicle battery on occasion.

Before it reaches the voltage regulator and is subsequently delivered into the battery, the diode rectifier converts alternating current (AC) to direct current (DC). After conversion, the battery may utilize the converted energy to recharge itself.

Conversion Of Mechanical To Electrical Energy

The crankshaft pistons ignite the gasoline pumped into the combustion chamber from the tank. The crankshaft directs the explosive energy of combustion to an alternator through a serpentine belt. While the alternator’s pulley rotates, mechanical energy is converted to electrical energy. Having a professional tighten your alternator belt can aid in keeping your alternator functioning smoothly.

(Video) Charging a dead car battery using the cars alternator

Powering Accessory

Although the alternator drives practically every electrical system component, the battery may provide some power. Electrical components in your automobile include power steering, power windows, lights, and wipers. Therefore, if you believe your alternator is damaged, use as little energy as possible until it is fixed.

How Many Volts Should A Car Battery Have When Fully Charged?

Automotive batteries that are fully charged should have a voltage of 12.6 volts or above. This reading should be between 13.7 and 14.7 volts while the engine is operating. If you do not have a multimeter, you may test your electrical system by starting the vehicle and turning on the headlights.

If they are faint, this indicates that the battery is powering the lights and that the alternator produces little or no charge. If the lights become brighter as the engine is revved, the alternator is producing some current but not enough at idle to keep the battery charged.

If the lights remain steady in brightness and do not alter in intensity while the engine is cranked, the charging system is most likely operating correctly. Whether you’ve been having battery system difficulties and the headlight test passes, you should check to see if the battery retains a charge or if anything on the vehicle is draining it.

Factors Affecting A Car Battery’s Charging Time

The time required to recharge a car battery varies considerably. The following are the relevant factors:

  • A well-maintained sulphuric acid and water battery charge more quickly than a battery with issues.
  • A 12 v battery charger will likely charge more quickly than a 24-volt battery.
  • In 4-5 minutes, a high-capacity charger can fully charge the battery. If the charging is slowed down, it might take up to 24 hours for a dead battery to be charged entirely.
  • Unlike idle, driving faster on the interstate rapidly charges the battery.
  • An alternator with greater power and fewer loads will charge a battery more quickly than one with inadequate power.


A functional alternator is crucial. Understanding How Quickly Does An Alternator Charge A Battery? And the numerous duties of an alternator can help you take better care of your vehicle and recognize any possible problems. After reading this article, you will understand precisely how long the alternator takes to charge the battery. I hope it proves beneficial to you.

Frequently Asked Questions

How Much Time Does an Alternator Need to Charge a Dead Battery?

As previously stated, various variables determine the length of time or distance required to recharge a battery. It may take up to 60 miles to completely recharge your battery, depending on your driving speed, alternator output, and battery capacity.

(Video) Deep Cycle Battery Charging with your Alternator: The 3 Best Options explained [+ Wiring Diagram]

Can the Alternator Recharge a Dead Battery?

Rather than charging a dead battery, alternators are designed to power continually running gadgets. Using an alternator to recharge a dead battery can prematurely fail the alternator.

How long does it take for a 12-volt battery to be charged by an alternator?

Charging periods vary according to battery type and charger. In an hour of driving, it may completely recharge a 12 v battery charging voltage charged by the car’s alternator. The power of an alternator varies between 45 and 200 amps; while a 10 amp battery charger how long takes between 4 and 11 hours to charge the battery completely.

Is the Alternator Charging the Battery While the Engine Idles?

Yes, when the engine is idle, the alternator charges the battery. So long as the engine crankshaft turns the alternator mechanically. Thus, the alternator can certainly manage 80 amps while idling, and it can charge a completely discharged battery to 80% in around two hours.

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How Quickly Does An Alternator Charge A Battery? Guide (2)

Mohammad Daim

Hi, I am Muhammad Daim – an automotive lover and researcher. I am a co-founder at I have a Bachelor’s Degree in Computer Science but cars and trucks have always been my passion. My goal is to always learn new skills and share my experience with the world.


At what rate does an alternator charge a car battery? ›

Car batteries range from 40AH to 110AH, and alternators range from 45 amps to 200 amps. If you are using an alternator, a 40 amp alternator will take half an hour or less to fully charge the battery, a 2 amp charger will take 2-4 days.

Will an alternator charge a battery at idle? ›

As what was mentioned it does charge the battery when idling however it will charge more efficiently when the vehicle is at a certain rpm. Where the alternator is rotating at a higher rpm to charge the battery.

Will alternator fully charge battery? ›

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.

How long should I let my car idle to charge battery? ›

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.

Does revving charge battery faster? ›

The battery will charge faster if you rev the engine faster. Why? Because the faster the crankshaft turns, the faster it turns the belt that runs the alternator. And the faster the alternator turns, the more electricity it produces to run all the electrical stuff in the car — and recharge the battery.

Can alternator drain battery while sitting? ›

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.

How long does it take an alternator to charge a 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.

Can a car battery recharge by sitting? ›

Keeping a car battery plugged in for twenty four hours can fully recharge your battery, and chargers are typically quite affordable.

How far do you have to drive to charge a battery? ›

If you want to get a full charge from a drive, you will need to drive at least half an hour on highway speeds. This is about 30 to 40 miles. You can also idle your car to get power, but it will take a far longer time.

What drains a car battery faster? ›

Electrical devices or lights left running, a defective charging system or alternator, and extreme weather are some common reasons but maybe it's just time to get a new battery.”

Does idling car drain battery? ›

As mentioned, your car's engine continues to consume fuel so long as it's powered on. But it also consumes power from your car's battery because the engine and alternator both run slowly whenever your car idles. The alternator provides enough power to charge the battery by itself.

What makes a battery charge faster? ›

To make a device charge faster, most manufacturers either boost the amperage or vary the voltage in order to increase the amount of potential energy. The majority of fast charging standards typically vary the voltage rather than boost the amperage.

What destroys a car alternator? ›

Strong vibrations or water ingress are possible causes of bearing damage on alternators. But too much tension on the drive belt can also cause bearing damage or premature wear.

What kills a alternator? ›

Most of the time, alternators fail as a result of age or use. However, some other factors can cause an alternator to fail prematurely. Fluid leaking on the car alternator can commonly lead to failure. Often, engine oil or power steering fluid can work its way into the alternator and cause it to malfunction or fail.

What could be draining my battery if it's not the alternator? ›

7 Things That Can Drain Your Car Battery
  • You left your headlights on. ...
  • Something is causing a "parasitic draw." ...
  • Your battery connections are loose or corroded. ...
  • It's extremely hot or cold outside. ...
  • The battery isn't charging while you drive. ...
  • You're taking too many short drives. ...
  • Your battery is old.
Feb 17, 2020

What tells the alternator to start charging? ›

These systems are controlled by the vehicle Engine Control Unit (ECU). As the vehicle demands more load the ECU sends a signal to the alternator requesting it to start charging. The alternator has to cope with varying electrical loads and adjust its charge rate accordingly.

Can you test an alternator without removing it? ›

Yes, you can test an alternator without removing it. You either use a multimeter to test the battery, listen for a squealing sound from the engine, or check for a fuzzy sound from your radio.

How fast does an alternator need to turn to charge a battery? ›

You need a minimum of 1000 revolutions per minute (RPM) from your engine to generate the power needed to charge your battery. Faster speeds generate more RPMs, so your battery will recharge faster at speeds of 55 MPH or higher.

How many amps per hour does an alternator charge? ›

Alternator ratings range from about 60 or 70 amps up to 150 amps or more on many late-model vehicles. Some high-output alternators can generate upward of 200 amps. The amp rating of the alternator is matched to the vehicle's electrical system.

How many amps should a 12 volt alternator put out? ›

An OEM alternator should put out about 65 amperes for most cars.

How long does it take an alternator to charge a 100AH battery? ›

The alternator is a voltage source and not a constant current source. Charging current is usually limited to 1/10 of the capacity. So for a 100AH battery this would be a maximum of ~10A. 10 Hours in theory, probably more from 0 to 100%.

What should a 12 volt battery read when fully charged? ›

12.6V volts or above - Your battery is healthy and fully charged.

Should I charge my battery at 2 or 10 amps? ›

If you want a faster battery charge rate, go with the 10 amps. Low charging current at 2 amps can be unreliable, but it won't hurt if you have two chargers.

How many amps do I need to charge a 12 volt battery? ›

A 12-volt automotive battery, for instance, takes a while to charge. In fact, fast charging for this kind of battery is not recommended. 10 amps are the recommended current.

What happens if you put a higher amp alternator on my car? ›

That is, your alternator will only supply the amount of amperage a particular component demands—and no more. So high-output alternators will not harm your components or charging system, no matter how high you go with the amps.

What is normal alternator output at idle? ›

A good alternator should produce about 13.5 to 14.5 volts with the engine idling. If the voltage reading is low (12.5 volts or less), it indicates a charging problem but does not tell you what's causing it.

Is a dual alternator better than a high output alternator? ›

Dual alternators are more efficient than single alternators, meaning they can produce more power. They also work better in heavy vehicles because they can handle more voltage and RPMs. For example, a single alternator has one electrical output, while a dual alternator has two.

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.

Will a higher amp alternator charge a battery faster? ›

An alternator with larger amperage output will recharge your batteries faster assuming your battery bank can take a faster charge rate.


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