A battery is a device that stores and provides electrical energy through chemical reactions. It consists of one or more cells, each containing positive and negative electrodes separated by an electrolyte. When a circuit is connected, a chemical reaction occurs within the battery, causing electrons to flow from the negative electrode (anode) to the positive electrode (cathode), generating an electric current that can power devices. Rechargeable batteries can reverse this reaction when connected to a power source, allowing them to be reused after recharging. Batteries are utilized in various applications, including portable electronics, vehicles, and backup power systems.