A battery stores and releases electrical energy through a chemical reaction known as electrochemical reaction. Inside a battery, there are two electrodes (usually made of different metals or metal compounds) immersed in an electrolyte solution (which can be an acid, alkaline, or an ion-containing liquid or gel).
During charging, an external electrical current is applied to the battery, causing a chemical reaction at both electrodes. At the positive electrode (known as the cathode), the metal or metal compound undergoes oxidation and releases electrons. At the negative electrode (known as the anode), another chemical reaction occurs where the metal or metal compound undergoes reduction and accepts electrons. This process stores electrical energy in the battery.
When the battery is connected to an external circuit (e.g., a device or a light bulb), the stored energy is released. The chemical reactions are reversed, and the electrons flow through the circuit from the negative electrode to the positive electrode, creating an electric current. This current can power the device connected to the battery.
The flow of electrons generates an electric potential difference between the electrodes, which is measured in volts. This potential difference determines the battery's voltage, which can vary depending on the specific chemistry and design of the battery.