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A battery is an electric power source commonly used to provide energy for a vast array of electric and electronic appliances. It is composed of two or more cells, each of which is a power-supply unit, having electrodes which are connected by a conducting medium. Batteries are primary cells when energy can be directly extracted from the chemical energy stored within and secondary cells when chemical energy is returned back to the battery through a charging process.

Batteries are essential in a world where there are many electronic or electrical appliances. Without some sort of reliable energy source, these appliances would be useless.