Does an Alternator Charge a Battery?

An alternator plays an important role in an engine. Does this include charging a vehicle’s battery?

Yes, an alternator charges a battery and a vehicle’s battery while driving. An alternator charges the batteries in all modern cars, while dynamos are common in older cars. Both types are driven by a belt that rests on a pulley extending from the engine. The principle is based on how an electromagnet induces a current in a wire.

Below I explain how an alternator works to charge a battery and also mention how long it takes for an alternator to charge it.

Alternator Components

An alternator consists of a stator and a stationary set of wire coil windings.

A rotor, which is an electromagnet, revolves inside. When a small amount of current passes through, the copper-carbon (or just carbon) brushes touch two revolving metal slip rings on its shaft. See the picture below.

The electromagnet’s rotational movement inside the stator coils generates electricity through alternating current (AC). The current is then rectified to flow in only one direction to provide a direct current (DC).

A warning light appears on the vehicle’s dashboard if the battery is not sufficiently charged. If you have a battery-condition indicator, it will show the battery’s current state of charge.

How an Alternator Works

An alternator works by converting mechanical energy into electrical energy.

The illustration below shows how the alternative and battery work together in a vehicle.

link between an alternator and a vehicle’s battery
The link between an alternator and a vehicle’s battery (1)

The electromagnet in the vehicle’s alternator generates electricity.

Electric current flows through the wire as the magnet moves past a closed loop. The magnet’s North Pole passes the top of the loop, while its South Pole passes the bottom. Together, they make the current flow in one direction around the loop.

As the poles move away, the current ceases momentarily until the situation is reversed, i.e., the South Pole is now at the top and the North Pole at the bottom. This makes the current flow again but in the opposite direction this time.

How Long Does an Alternator Take to Charge a Battery

Table: Factors Affecting Alternator Charging Time

FactorsEffect on Charging Time
Type of alternatorVaries depending on specifications
Battery sizeLarger batteries take longer
Battery ageOlder batteries take longer
Engine RPMHigher RPMs charge the battery faster
Vehicle speedDriving the vehicle helps to charge the battery faster

It depends on certain factors if you’re wondering how long an alternator takes to charge a battery.

The main factors are the type of alternator and the battery’s size and age. Normally, an alternator takes 30 minutes and one hour to charge a battery while driving fully. It will take longer if you try to charge it while idle, i.e., with the engine running, without driving the vehicle. If you leave it idling for a couple of hours, you will probably achieve only 80% charge, so it’s better to take the vehicle for a drive to make the battery charger quickly.

Alternatively, you could step on the gas to increase the engine’s RPM. This would make the battery charge quicker without going anywhere.


(1) Popular Science. Bonnier Corporation. Jun 1980. Vol. 216, No. 6.

Image and Video References


Technical Automobile

How helpful was this article?

Were Sorry This Was Not Helpful!

Let us improve this post!

Please Tell Us How We Can Improve This Article.

About Alex Robertson

c3c9d43f1f0d14c4b73cb686f2c81c4e?s=90&d=mm&r=gCertifications: B.M.E.
Education: University Of Denver - Mechanical Engineering
Lives In: Denver Colorado

Hi, I’m Alex! I’m a co-founder, content strategist, and writer and a close friend of our co-owner, Sam Orlovsky. I received my Bachelor of Mechanical Engineering (B.M.E.) degree from Denver, where we studied together. My passion for technical and creative writing has led me to help Sam with this project.

| Reach Me