A device that can directly convert chemical energy, light energy, heat energy, etc. into electrical energy is called a battery. It also includes types such as chemical cells, solar cells, nuclear cells, etc. Generally, the term battery refers to a chemical cell.

　　Practical chemical batteries are divided into primary batteries and batteries. Most of the batteries we come into contact with in our daily lives are batteries. Before using a battery, it needs to be charged first, and then discharged for use. During charging, it converts electrical energy into chemical energy, and during discharge, chemical energy is converted into electrical energy.

　　When the battery is discharged, the current flows from the positive electrode through the external circuit to the negative electrode. In the electrolyte, positive and negative ions migrate to both electrodes, and the current flows from the negative electrode to the positive electrode. During discharge, both electrodes undergo chemical reactions, and the circuit breaks or the chemical reactants are depleted, which will stop discharging.

　　According to the different substances used inside the battery, there are rechargeable and non rechargeable batteries. Some chemical reactions are reversible, while others are irreversible.

　　The storage and discharge capacity and speed of a battery are closely related to its material.