How Long Does an Alternator Take to Charge a Battery

Published on: May 22, 2022
Written by Liam Jaxon / Fact-checked by David Rowan

In order to charge your battery, the alternator must generate a voltage that is slightly greater than the battery voltage, which causes the current to flow into the battery until the battery achieves the higher voltage. But do you know how long an alternator takes to charge a battery?

Faster battery charging is a benefit of using an alternator. It takes 30 minutes to recharge the battery on the highway, but an hour or more in the city. If you have a good alternator, you should be able to charge a flat battery to 80 percent capacity in roughly 2 hours.

how long does an alternator take to charge a battery

About 14.2V is the maximum charge that can be applied to a fully charged 12v battery. The alternator determines how quickly the battery is charged. Many people believe that the car’s battery is responsible for all of the vehicle’s electrical needs.

On the other hand, the alternator is responsible for ensuring that everything functions correctly. Instead, a small number of us may worry, Can a bad alternator ruin a battery? This article will provide you with all the information you require regarding the duration of charging a battery by alternators.

What Is an Alternator?

An alternator is a device that produces electricity. The alternator’s job is to transfer power to the vehicle and replenish its power supply by recharging the battery. There is no car on the road today that does not have an alternator, except a few hybrids and internal combustion engines. 

It is common for the alternator to be situated near the front engine and enclosed by a strap. The most frequent question we got is, can a bad alternator cause battery corrosion? Of course, it happens when a battery cell is defective, it might cause overcharging. So knowing the details of an alternator is crucial.

Parts and Pieces of an Alternator

An alternator’s components are designed to provide the vehicle with the proper power. The key components and their roles of your car’s charging system are as follows:

Stator And Rotor

An internal magnetic field pulls the rotor and stator together, spinning the rotor around and around in the stator’s copper wiring. It is the movement of magnets over the wire that generates electricity.

A Rectifying Diode

Diode rectifiers transform alternator voltage into a form usable by batteries for recharging.

The Voltage Regulator

The voltage regulator is responsible for ensuring that the alternator’s output voltage is maintained. It monitors the battery voltage and distributes power to the rest of the vehicle.

Cooling Fan

It is necessary to cool the heat generated by alternators. In addition to the vents and metal shell, they have revolving fans for extra cooling. For older models, the fan blades are usually exterior.

The Function of an Alternator

The alternator is a crucial part of your car’s power system, but it’s important to remember that batteries go bad considerably more frequently than alternators. An alternator’s primary job is detailed in the following:

Produces Electricity

The voltage of a car’s battery fluctuates according to the state of the engine. Before knowing how the alternator produces electricity, it’s essential to know how many volts is a car battery(car battery voltage chart). A combustion engine produces electricity. Most modern cars use a serpentine belt to drive the alternator, and the belt’s movement provides mechanical energy to the alternator’s rotor.

The rotor generates electricity as it turns. The rotor’s magnets create a magnetic field when they travel over the stator’s copper wires. This magnetic field produces and stores a voltage in a stator. The voltage regulator then distributes and controls the voltage to the battery.

Charge the Battery

There must first be a change in the format before the battery can take advantage of the alternator’s output. This is due to the fact that electricity can flow in multiple directions. Alternators produce alternating current (AC) electricity, which can occasionally flow in the opposite direction of what is generated by a car battery.

The diode rectifier converts AC electricity to direct current (DC) before it gets to the voltage regulator, then sent into the battery. The battery can then use the energy to replenish itself after being converted.

Mechanical to Electrical Energy Conversion

The crankshaft pistons burn the fuel that is poured from the tank into the combustion chamber. The crankshaft sends the combustion’s explosive energy to a serpentine belt attached to the alternator. Mechanical energy is transformed into electrical energy while the alternator’s pulley spins. Having your alternator belt tensioned by a professional will assist in maintaining your alternator running smoothly.

Accessories Powering

The alternator powers nearly every electrical system component, but the battery can supply some power. Power steering, power windows, lighting, and wipers are among the electrical components in your car. So, if you think your alternator is broken, use the least amount of electricity possible until it is repaired.

Factors Influencing the Charging Time of a Car Battery

Car battery recharging times might vary widely. Followings are the factors:

  • A well-maintained battery with sulphuric acid and water charges faster than a battery with difficulties.
  • A 12-volt battery may charge faster than a 24-volt battery.
  • A high-capacity charger can fill the battery in 4-5 minutes. It can take up to 24 hours for a dead battery to be fully charged if the charging is slowed down.
  • Engine RPM- unlike idling, driving faster on the highway charges the battery quickly.
  • An alternator with more power and less load will charge a battery faster than one with insufficient power.

Alternator We Recommend for Quickly Recharging a Battery

Amazon LinkCapacityAMPSWeight Compatible With
[amazon link=”B00IZYTCLG” title=”Remy 94125 New Alternator” /]14.4V10513.0 poundsHonda Accord, Ford
[amazon link=”B001UC3BIK” title=”Bosch AL0843X Alternator” /]12V180‎9.02 poundsVolvo, Nissan, Sprinter,Porsche carrera
[amazon link=”B007QBQWTO” title=”ACDelco Gold 335″ /]13.8v 10510.2 poundsSilverado, Savana, Pickup, Cadillac Escalade
[amazon link=”B00SHU8EJE” title=”Remanufactured DB Electrical 400-52270R Alternator” /]12V13012 poundsHonda Accord, Crosstour 
[amazon link=”B07RWZ64KR” title=”OCPTY Alternators 11099″ /]12V130‎12.54 poundsACURA Auto and Light Truck, HONDA Auto and Light Truck
[amazon link=”B001G9G774″ title=”Powermaster 7294 Alternator” /]14.8 volts10011 poundsWagoneer, Chevy G20 van


1. How Long Does It Take an Alternator to Charge a Dead Battery?

As previously said, several factors influence how long or how far a battery needs to be recharged. It can take up to 60 miles to fully recharge your battery, depending on various factors like your driving speed, alternator power, and battery capacity. 

2. Will the Alternator Charge a Completely Dead Battery?

Instead of recharging a dead battery, alternators are made for powering devices that run continuously. Using an alternator to charge a dead battery will cause the alternator to fail early.

3. How long does it take an alternator to charge a 12-volt battery?

Charging times are dependent on the battery and charger. A 12-volt battery charged by the car’s alternator may be entirely recharged in an hour of driving. An alternator’s output ranges from 45 to 200 amps, and a 10 amp charger takes 4-11 hours to fully charge the battery. 

4. Does the Alternator Charge the Battery While Idling?

Yes, the alternator charges the battery while idling. So long as the alternator is mechanically turned by the engine crankshaft. So the alternator can probably handle 80 amps at idling, and a flat battery may be charged to 80% in around 2 hours.

5. What Drains a Car Alternator?

When your alternator’s diode fails, your battery will begin to deplete. The circuit may continue to charge even after the alternator diode has failed, resulting in the engine shutting off.


It is critical to have a functioning alternator. Understanding how long an alternator takes to charge a battery and its various functions will help you better care for your vehicle and identify any potential issues that may arise. 

After reading this essay, you know exactly how long it takes the alternator to charge the battery. I hope you find it useful. 

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About This Writer

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Hi, I am responsible for the 'Homeowners Power Solutions' category. My name is Liam Jaxon and a licensed technician with 7 years of experience in vehicle batteries, electrical gadgets, and home appliances. My working experience in different residential & light commercial electrical sectors and the automobile industry helped to acquire vast knowledge in this industry.

Hi, I am responsible for the 'Homeowners Power Solutions' category. My name is Liam Jaxon and a licensed technician with 7 years of experience in vehicle batteries, electrical gadgets, and home appliances. My working experience in different residential & light commercial electrical sectors and the automobile industry helped to acquire vast knowledge in this industry.

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