A battery is a portable store of electrical energy. This energy is stored in the form of chemicals.
A battery is made up of chemicals that react together. The chemicals are separated by a barrier. These chemicals exchange electrons but they can not do it across the barrier. When a wire is connected from one end of the battery to the other electrons flow through the wire to the other side. If the wire is connected to a light globe or radio, the electrons make the light globe and radio work as they pass through them. In the case of the light globe electrical energy is transformed into light and heat.

Click to see a chemical reaction producing electric current. In this 120kb movie clip magnesium and copper metal react in concentrated sulfuric acid to produce electrons that flow through the light globe.