What Is the Function of Sulfuric Acid in Car Batteries? 

 September 19, 2021

By  Phil Borges

Car batteries generally tend to come in the form of lead-acid batteries and contain several components. One such component of car batteries includes sulfuric acid.

Sulfuric acid is used in car batteries to serve as an electrolyte in combination with water that aids the reaction that tends to take place in the battery to allow ions to flow from one terminal to another. While sulfuric acid is a significant component in the car battery, it may also lead to some issues.

It is important to remain cautious of such issues when it comes to your car battery. If you want to find out more about these as well as about the detailed function of sulfuric acid, you can keep reading the following sections of this article.

Why Is Sulfuric Acid Used in Car Batteries?

Sulfuric acid plays an important role in aiding the chemical processes and reactions that take place inside the lead-acid battery of a car. In combination with water, sulfuric acid forms an electrolyte in the car battery.

Inside this battery, a process takes place that converts chemical energy into electrical energy wherein a movement of electrons takes place between the negative and positive electrodes of the battery.

The direction of this movement is generally determined by the process being performed, which could include charging or discharging through usage. During the charging process, sulfuric acid gets discharged into the electrolyte but gets used up during the discharging process.

The chemical reaction that takes place inside the battery with the assistance of sulfuric acid can be summed up through the following steps:

Once the electrons from the negative terminal reach the positive terminal, the sulfate formed from the sulfuric acid makes its way to the negative terminal and forms lead sulfate by combining with lead.

Similarly, lead sulfate gets formed in the positive terminal as well, while the electrolyte supports the formation of water due to the presence of oxygen that arrives through the positive terminal.

This reaction can thus lead to the usage of the battery in the functioning of the car.

After a point, the battery will need to be charged, which will reverse the process and bring back the sulfuric acid to the electrolyte.

How Much Sulfuric Acid Is Present in Car Batteries?

Sulfuric acid is generally present alongside distilled water in car batteries. Usually, 30%-50% of sulfuric acid is contained in the electrolyte in car batteries while the rest of it is water.

The density of this sulfuric acid tends to be around 1.25 kilograms per liter with varying levels of concentration (usually around 30%-35%).

The level of this sulfuric acid tends to fluctuate in the electrolyte throughout the discharging and charging processes in a cyclical way.

Should You Add More Sulfuric Acid?

Throughout the process, it is important to maintain a certain level of the electrolyte to allow the battery to function up to its given lifespan. During this time, however, you should not add additional acid to the electrolyte but should only top it up with distilled water.

In case of leakages or spills, you can consult a professional and ask them to fill in the acid for you if they recommend it. In modern batteries, however, the need to consistently fill up the water has also reduced significantly.

It is normal for the content of sulfuric acid to keep fluctuating inside the electrolyte. While the discharging process takes the acid away from the electrolyte, the charging process brings it back to it.

However, as time goes on, this is bound to reduce the overall content of sulfuric acid in the electrolyte due to small amounts of dissipation that take place each time. This also ends up reducing the efficiency of the battery itself, reducing the number of charging cycles remaining in the battery.

Potential Issues

Despite the importance of sulfuric acid in the electrolyte of the car battery, there are also certain issues that can arise due to the presence of the acid:

In case charging does not take place in the required way, or if the voltage level during the charging process is insufficient, this can lead to an occurrence known as layering.

This layering can separate the water from the acid in the electrolyte, leading to a small amount of it being used during the discharging and charging processes. If this happens too frequently, the overall lifespan of the car battery can reduce significantly.

Sulfation can also take place when a low voltage is presented while charging. This results in the crystallization of the lead sulfate that forms at the negative and positive terminals.

If this kind of crystallization occurs, it becomes difficult for the reaction to reverse itself, preventing the sulfuric acid from returning to the electrolyte. This reduces the lifespan of the battery while also preventing it from recharging appropriately.

In case of overheating or cracks, leakages or spills may also occur, causing the sulfuric acid to release out into the open. This can lead to several damages to the battery and the engine while also causing potential health hazards in case you come into contact with it.

It is important to regularly clean and maintain the battery to prevent these issues from occurring. Proper charging methods must also be used.

Frequently Asked Questions

Why does sulfuric acid in a car produce electricity?

Sulfuric acid in a car produces electricity in order to allow the battery to start up and use the car engine efficiently. Its presence is important to convert chemical energy into electrical energy so that this can take place.

It is equally important for the electrical energy to turn back into chemical energy so that the sulfuric acid can continue to produce electricity through its ions at the terminals of the battery.

It is essential that these processes can take place well throughout the lifespan of the battery, although the efficiency is bound to reduce over time due to wastage that normally takes place during these processes.

Can any other acid be used in a car battery?

Sulfuric acid is the best kind of acid that can work efficiently in a car battery, generally because such car batteries have a lead-acid composition. It is important, therefore, for the acid to be compatible with the lead so that it can combine and decompose well with it.

Not being able to react well with the element can lead to several issues with the car battery, ranging from inefficiency, leakages or even explosions.

It is, however, possible for other acids to be used inside the car battery as long as they meet the necessary requirements. Since sulfuric acid is less expensive and easily available, it is also preferred by producers.

What form is the electrolyte available in?

Most commonly, the electrolyte comes in its usual wet form wherein it involves a combination of the water with the sulfuric acid.

However, with new innovations and technologies, several car batteries can also have the electrolyte in the form of a gel or a stable mat that provides improved efficiency throughout the charging and discharging processes.

These technologies can further prevent too much wastage or losses during this process while also solving the issues of layering and, occasionally, sulfation. This can be highly advantageous to improve the lifespan of car batteries.

Does sulfuric acid require certain conditions to function well?

It is important for the sulfuric acid and the car battery, in general, to be kept in cool enough temperatures. Extreme temperatures could reduce the efficiency of the battery, whether that includes extreme heat or extreme cold.

There are also some substances that might be incompatible with the acid, which is why it is important for you to keep the battery covered and well protected throughout.

Contact with such substances as metals can be hazardous, leading to fires, explosions or spillage.

Is it possible to maintain the condition of the electrolyte?

While natural wear and tear are natural, you can maintain the efficiency of the battery through regular cleaning. Several additives such as chemicals are also added during the production process that can help prevent major issues with the electrolyte.

About the author

Hi, I'm Phil Borges.. thanks for reading.. My wife says I can't shut up about batteries so to save my marriage I've started this blog .. where I'd be ranting about batteries! Please leave a comment if you have any questions, I'm happy to help!

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