Car Battery: Structure, Function, Classification, Operating Principle

- Car Battery: Structure, Function, Classification, Operating Principle
Latest update date: February 24, 06

The quality of car batteries contributes to the efficient operation of the car. Through this article, Thanh Phong Auto will provide the most basic information about batteries, helping users clearly understand what car batteries are, their classification and main functions. 

1. What is a car battery?

Car batteries have the function of storing electricity to provide energy for the starting device (starter) and ignition system, among other systems. At the same time, supply power to loads in case the generator is not working or the engine rpm has not reached the specified speed. Moreover, the battery also has the effect of providing power when the loads use current exceeding the generator's prescribed level.  

2. Classification of batteries

Currently, most car batteries use lead batteries. They are divided into two main types: sealed batteries (dry batteries) and open batteries (water batteries). If the car owner can add water to the water battery, then the dry battery will be completely opposite, they usually do not need maintenance and will be used until they break.  

2.1 Dry battery

This type of battery is sealed so there is no need to periodically add water. Dry batteries are basically not completely dry but contain H2SO4 solution in a thick gel form. 

- Car Battery: Structure, Function, Classification, Operating Principle

Figure 1: Dry battery 


  • There is no need to waste time adding more solution or doing maintenance because the acid solution is already available and pre-filled.  
  • When left unused for a long time, dry batteries consume less electricity than water batteries, so they can be used for a long time. 
  • Does not cause unpleasant odors due to sealed structure. 
  • No regular maintenance required. 
  • Fast voltage recovery time due to high charging current.  
  • During use, there is no need to add additional electrolyte. 
  • Highly durable due to being manufactured using new technology.  
  • Cleaner and safer than water batteries because they have a sealed structure, so there is less risk of corrosion due to escaping acid vapors. 


  • Due to modern advanced production technology, it must be imported from abroad, so the price is quite high. 
  • Batteries have a major disadvantage of suddenly running out of power, so users need to regularly pay attention to the battery's condition to avoid running out of power while on the move.  

2.2 Water battery

This is a type of battery that has sulfuric acid solution inside, and has a maintenance cap to add distilled water.  

- Car Battery: Structure, Function, Classification, Operating Principle

Figure 2: Water battery 


  • When properly cared for, it will be highly durable. 
  • Cheap price due to simple structure. 
  • After a long time, the power can still be restored automatically. 


  • Needs to be checked and maintained periodically to avoid running out of fluid to help the battery last longer. The periodic inspection period is every 3 months for short-distance vehicles and 1 months/time for long-distance vehicles. 
  • If the battery is not connected to electrical equipment, it needs to be recharged every 3 months. 
  • Causes unpleasant smelling gas due to unsealed structure. 
  • Lifespan is lower than dry batteries. 
  • When the acid evaporates, it can cause rust inside the lid, making it unsafe to use 
  • With the above characteristics, today most car users often choose to use dry batteries because they do not need regular inspection or maintenance but are safer to use. Particularly for large trucks, they often use water batteries because they have a larger output current than dry batteries.      

3. Structure and operating principles of car batteries

It can be seen that the battery is an important part of the car, so it is necessary to clearly understand its structure, functions and operating principles. 

3.1 Structure of car battery

The structure of a car battery will be divided into internal structure and external structure. The details in the battery will create a complete whole to achieve the best operating results. 

- Car Battery: Structure, Function, Classification, Operating Principle

Figure 3: A car battery will have an internal and external structure (Source: Collected) 

The internal structure of a car battery includes: 

  • The negative and positive plates contain separation plates and are connected by connecting rods.  
  • There are many small compartments and each compartment contains H2S04 solution. 

- Car Battery: Structure, Function, Classification, Operating Principle

Figure 4: The internal structure of a car battery includes many acid compartments (Source: Collected) 

As for the external structure, it includes the following details: 

  • The shell is usually made from hard rubber or bitumen material because these materials have high thermal insulation and anti-corrosion properties and great mechanical strength. 
  • The most recognizable feature of a battery is that there are 2 protruding poles above the positive and negative poles of the battery, usually the terminal covers have colors to distinguish such as: red is the positive (+) pole; Blue is the negative pole (-). 

- Car Battery: Structure, Function, Classification, Operating Principle

Figure 5: External structure of a battery with 2 protruding poles at the top (Source: Collected) 

3.2 Operating principles of car batteries

Car batteries operate on the principle of charging and discharging through a chemical reaction with an electrolyte solution.  

- Car Battery: Structure, Function, Classification, Operating Principle

Figure 6: Operating principle of a car battery (Source: Collected) 

When discharged, the battery will provide an electric current to the consumer. When the acid in the electrolytic solution reacts with lead, it turns into water, causing electrical energy to be released. At that time, sulfuric acid along with the negative and positive plates is converted into lead sulfate. The discharge process causes the amount of water to increase but reduces the amount of sulfuric acid, causing the electrolyte concentration to decrease and the plates gradually approach the outside due to the nature of PbSO4, causing the potential difference between them to gradually decrease.  

When charging, the electrolyte concentration increases, the electrolyte changes into sulfuric acid. Along with that, the positive plates will turn into lead oxide, and the negative plates will turn into lead. At this time, the direction of the charging current is opposite to the discharge current.  


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