The three main parts of the dry cell battery are the positive electrode (cathode), the negative electrode (anode) and the electrolyte. The battery design does not allow the anode and cathode to come in direct contact. The electrolyte, which acts as a barrier, prevents the anode and the cathode from reacting with each other within the cell.
The dry cell began life as a wet cell. Luigi Galvani first made some observations on the electrical arc created by connecting a frog's legs by an arc composed of brass and iron. Alessandro Volta worked with non-living materials to create the "voltaic pile"---the first device to produce an uninterrupted current. The electrochemical principles established are still valid. In the 1880's, Carl Gassner made the first commercially viable dry cell. The dry cell as we know it now began as the Columbia dry cell made by the National Carbon Corporation, which became the Energizer Battery Company. This was a sealed 1.5-volt cylindrical, paper-lined unit.
The dry cell is durable, maintenance-free and inexpensive. It contains no liquids so there is no leakage. It is a sealed unit and is reliable. A power plant may suffer an outage but a dry cell will supply power as long as its chemicals have not run out. It has a long shelf life. Attach it with the proper polarity to your device and you get instant power.
"Imagine a world without batteries!" Mary Ellen Bowden writes in her book "Chemistry is Electric." "A teenager walks outside wearing headphones, tethered to home by a lengthy extension cord. An old man winds his pacemaker like a pocket watch ... In thousands of ways, large and small, batteries have changed our daily lives."
From transistor radios to underwater flashlights to powering implantable devices and appliances used in outer space, dry cell batteries have become the power source of choice.
A battery's shelf life depends on its self-discharge rate--the rate at which the chemical components react with each other. Most of the commonly used batteries have a slow self-discharge rate and hence a very slow consumption of the chemicals. Remember that the chemical reactions that deplete the life of the battery occur when the battery is used. Look to use a battery within four to five years from date of manufacture.