A battery is made up of three parts:
Negative side (called an anode)
Positive side (called a cathode) and
An electrolyte (most often a liquid)placed between the anode and the cathode
When in physical contact, the anode reacts spontaneously with the cathode. In a battery though, the two elements are separated by the electrolyte. This reaction only needs an electrical contact between the two sides of the battery to occur. Therefore as we place the battery into our device, this energy is released as electrons moving through the circuit from the anode to the cathode: electricity to power our device!
As an example, our Alkaline batteries are composed of the following elements: Zinc as an anode, which reacts with Manganese oxide as a cathode, with a aqueous alkaline solution as the separating electrolyte.