Primary Cell Batteries
Combinations of certain metals, such as copper and zinc, will produce electrical activity when placed in special solutions called electrolytes. The two metals form the electrodes. The electrolyte creates a chemical action that causes the zinc to form positive ions and the copper to form negative ions. These ions are freely flowing in the electrolyte. No current flow can occur until the electrode terminals are connected to a circuit, like a light bulb. The electrons then flow from the zinc electrode through the external circuit to the copper electrode. The chemical reaction between the zinc and the electrolyte continues, and the zinc is eventually used up in the process.
Common dry cell batteries work on a similar principle with a paste-like electrolyte and a carbon electrode rather than copper.