what is battery

A battery is a device that converts chemical energy contained within its active materials directly into electric energy by means of an electrochemical oxidation-reduction (redox) reaction. The chemical reactions in a battery involve the flow of electrons from one material (electrode) to another, through an external circuit, providing an electric current that can be used to do work. A battery is made up of one or more electrochemical cells connected in series or parallel, depending on the desired output voltage and capacity. The positive terminal of a battery is the cathode, and the negative terminal is the anode. When a battery is connected to an external electric load, a redox reaction converts high-energy reactants to lower-energy products, and the free-energy difference is delivered to the external circuit as electrical energy. The term "battery" originally referred to a device composed of multiple cells, but it has evolved to include devices composed of a single cell.