According to the MIT School of Engineering, a battery provides an electrical charge due to the chemical reactions that take place inside it once it is connected into an electrical circuit. When a circuit connects the positive and negative poles, the anode and cathode inside the battery react with the electrolyte medium separating the two, producing a flow of electrons. This creates an electrical current and provides power.
There are three major components inside a battery. The anode is the negatively charged terminal of the battery, while the cathode is the positively charged terminal. The anode and cathode are not directly connected, but both are in contact with an electrolyte liquid or paste that allows electrons to pass from one to the other. When connected in a circuit, the anode reacts with the electrolyte to release electrons, and the cathode reacts with the electrolyte to absorb them. This produces a one-way flow of electricity through the circuit until the electrolyte medium is exhausted.
In batteries that are not rechargeable, the components undergo irreversible chemical changes as the electricity is discharged. Once the battery's electrolyte is depleted, the battery can no longer produce electricity. Rechargeable batteries use a reversible chemical reaction, allowing the battery to return to its initial state when recharged with a current.