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Imagine a world without batteries. All the devices we depend so much on would be useless! We’d only be able to take our laptops and phones as far as the reach of their cables, and then we are out of power. If batteries are so important, then what are Batteries?

A battery is a device that converts chemical energy contained within its active materials directly into electric energy using an electrochemical oxidation-reduction (redox) reaction. This type of reaction involves the transfer of electrons from one material to another via an electric circuit.

Although the term “battery” is often used, the cell is the actual electrochemical unit used to generate or store electric energy. A cell is a single unit that produces electricity through some method. Generally speaking, cells generate power through a thermal, chemical, or optical process.

A typical cell has two terminals (referred to as electrodes) immersed in a chemical (referred to as the electrolyte). The two electrodes are separated by a porous wall or bridge which allows electric charge to pass from one side to the other through the electrolyte. The anode—the negative terminal—gains electrons while the cathode—the positive terminal—loses electrons. This exchange of electrons allows a difference in potential or voltage difference to be developed between the two terminals—allowing electricity to flow. 

When you connect a battery's two electrodes into a circuit (for example, when you put one in a flashlight), the electrolyte starts buzzing with activity. Slowly, the chemicals inside it are converted into other substances. Ions (atoms with too few or too many electrons) are formed from the materials in the electrodes and take part in chemical reactions with the electrolyte. At the same time, electrons march from one terminal to the other through the outer circuit, powering whatever the battery is connected to. This process continues until the electrolyte is completely transformed. At that point, the ions stop moving through the electrolyte, the electrons stop flowing through the circuit, and the battery is flat


The chemical reactions in the battery cause a buildup of electrons at the anode. This results in an electrical difference between the anode and the cathode. You can think of this difference as an unstable build-up of the electrons. The electrons want to rearrange themselves to get rid of this difference. But they do this in a certain way. Electrons repel each other and try to go to a place with fewer electrons.

In a battery, the only place to go is to the cathode. But the electrolyte keeps the electrons from going straight from the anode to the cathode within the battery. When the circuit is closed (a wire connects the cathode and the anode) the electrons will be able to get to the cathode. In the picture above, the electrons go through the wire, lighting the light bulb along the way. This is one way of describing how electrical potential causes electrons to flow through the circuit.

However, these electrochemical processes change the chemicals in the anode and cathode to make them stop supplying electrons. So, there is a limited amount of power available in a battery.

When you recharge a battery, you change the direction of the flow of electrons using another power source, such as solar panels. The electrochemical processes happen in reverse, and the anode and cathode are restored to their original state and can again provide full power.

Different Types of Batteries

All the electrochemical cells and batteries are classified into two types:

-Primary (non-rechargeable)

-Secondary (rechargeable)

Even though there are several other classifications within these two types of batteries, these two are the basic types. Simply speaking, Primary Batteries are non-rechargeable batteries i.e., they cannot be recharged electrically while Secondary Batteries are rechargeable batteries i.e., they can be recharged electrically.


Batteries generally can be classified into different categories and types, ranging from chemical composition, size, form factor, and use cases, but under all of these are two major battery types;

1.      -Primary Batteries

2.      -Secondary Batteries

Let's take a deeper look to understand the major differences between Primary batteries and Secondary batteries.

1.       Primary Batteries

Primary batteries are batteries that cannot be recharged once depleted. Primary batteries are made of electrochemical cells whose electrochemical reactions cannot be reversed.

Primary batteries exist in different forms ranging from coin cells to AA batteries. They are commonly used in standalone applications where charging is impractical or impossible. A good example of this is in military-grade devices and battery-powered equipment. It will be impractical to use rechargeable batteries as recharging a battery will be the last thing in the mind of the soldiers. Primary batteries always have high specific energy and the systems in which they are used are always designed to consume a low amount of power to enable the battery to last as long as possible.

The most popular type of primary battery is an alkaline battery. They have high specific energy and are environmentally friendly, cost-effective, and do not leak even when fully discharged. They can be stored for several years, have a good safety record, and can be carried on an aircraft without being subject to UN Transport and other regulations.

Secondary batteries are batteries with electrochemical cells whose chemical reactions can be reversed by applying a certain voltage to the battery in the reversed direction. Also referred to as rechargeable batteries, secondary cells unlike primary cells can be recharged after the energy on the battery has been used up.

They are typically used in high drain applications and other scenarios where it will be either too expensive or impracticable to use single charge batteries. Small capacity secondary batteries are used to power portable electronic devices like mobile phones, and other gadgets and appliances while heavy-duty batteries are used in powering diverse electric vehicles and other high drain applications like load levelling in electricity generation.

Secondary batteries can be further classified into several other types based on their chemistry. This is very important because the chemistry determines some of the attributes of the battery including its specific energy, cycle life, shelf life, and price to mention a few.

The following are the different types of rechargeable batteries that are commonly used


Nickel Cadmium(Ni-Cd)

Nickel-Metal Hydride(Ni-MH)


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