Are Car Batteries DC or AC?

Automotive Lead-Acid Batteries: Performance and Longevity

What Is Car Battery?

Car battery is a rechargeable battery that is used for starting a motor vehicle, whose main purpose is to offer electric current to the electric-powered starting motor. It is in turn the starting chemically-powered internal combustion engine that indeed propels the vehicle. Once the engine is working, with the alternator charging the battery as demands increase or decrease, the power for the vehicle’s electrical systems is still offered by the battery. Below we can analyze if the car battery is a DC battery or AC battery.

DYVINITY Car battery

(Dyvinity car battery)

DC Battery and AC Battery

DC Battery:

Direct current, which is also called DC, is the electricity flowing in a constant direction or possessing a voltage with constant polarity either positive or negative. DC is the type of electricity made by a battery, which current passes from the positive terminal to the negative terminal and makes DC ranks higher than AC is the storage of the current. DC is stored more easily especially on a small scale. At times you need to store the electricity for the later use so that directly current scores better in this regard. On the other hand, Direct Current (DC) describes electrical current that only flows in a single direction.

DC graph 1

(DC graph)

For the reason that DC flows in a single direction, it’s primarily used in electronics. The single direction flow is utilized to control the transistor, which is the main building block of electronics. As a general rule of thumb, remember that everything runs off a battery, an AC adapter or a USB cable relies on DC.

AC Battery:

There are sources of electricity that produce voltages and currents which are alternating in nature, that is, it could cyclically change the directions. You must have learned about the generation of electricity by a generator either as voltage switching polarity or as a current switching direction, back and forth. This kind of electricity is called alternating current or AC.

The alternating current has an advantage over direct current as the voltage of AC can be easily transformed into a higher or lower voltage level after performing certain actions, but it is difficult to achieve with direct current. This is the reason that in most of the houses, buildings, and offices, alternating current is used as a source of electricity.

Compared with DC, AC describes the flow of electrical charge that changes direction periodically. 

AC graph 2

(AC graph)

Primarily, AC is used to generate electrical current and deliver power to buildings. That’s the case because transporting AC over large distances is significantly easier and more efficient when compared to DC.

Are Car Batteries DC or AC?

By now, you are fully aware of the difference between the AC and DC battery so now let’s move to the actual discussion that is whether the car battery is AC or DC. Therefore, in cars, we use DC battery for the reason that the current in the DC battery flows in one direction which is quite suitable for car mechanics.

Here is why the car uses a DC battery. Within the car battery, the process goes on with the chemical reaction. These batteries use lead-acid. For electrodes, they use a lead and for electrolytes, they use sulphuric acid and distilled water.

There are two plates in the battery which are immersed in the electrolyte. The electrolyte in return initiates a reaction between the two plates. As a result of this, a chemical reaction takes place which produces electrons. These electrons move between the two plates and, as a result, produce electricity.

AC changes its direction several times in a second that is known as frequency, so it cannot work in the car batteries as there is no possibility of inverting the electrodes. In such a case, only the direct current is valid and works the best. The car batteries get charged by the alternator while running. It happens at times, that you leave the car headlights on for the whole night, and in the morning you have to bear the dead battery. Thus, this indicates that the car battery cannot run for a longer period without being charged, which gets charged side by side while running.


The car’s electrical system is a tough subject, which is easy to get confused, but to conclude that all car batteries are DC. The reason for that is that we only cannot store AC in batteries.

Last but not the least, if we would connect an AC supply to a battery in order to store the AC, the battery would only charge during the positive half cycle and discharge during the negative half cycle. So, the average current or voltage in a full cycle would equal zero, meaning there is absolutely no way to store AC in a car battery.

Actually, you can’t actually store DC either, since electricity in its regular form cannot be really stored in any significant quantities. We actually convert DC into chemical energy in order to store it in a car battery, but I’m not going to get into that as it’s way too complicated for this article, which I intend to keep rather simple and easy to understand. To sum up, a car battery is a DC battery.

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