Batteries commonly used in radios, recorders, cameras, electronic clocks, toys, etc. are classified as dry batteries. The electrolyte in a dry battery is a non flowing paste, which is called a dry battery (see Figure 1), compared to batteries with a flowing electrolyte.

　　The outer shell is a cylindrical container made of zinc, with a carbon rod standing in the center of the zinc cylinder and a copper cap fixed at the top of the carbon rod. Carbon rods and zinc cylinders are called the electrodes of dry batteries. The carbon rod that gathers positive charges is called the positive electrode (symbol+, indicating the positive electrode of the battery), and the zinc cylinder that gathers negative charges is called the negative electrode (symbol -, indicating the negative electrode of the battery).

　　The basic principle of discharge: magnesium dioxide is filled around the carbon electrode, the zinc electrode forms the outer shell of the dry battery, and the carbon electrode is placed in the center. Electrons are given by electronized zinc metal (oxidation) and flow into external circuits to reach the carbon electrode. Magnesium dioxide near the carbon electrode receives electrons (reduction) to generate hydroxide ions and forms a new compound called magnesium oxide. The oxidation reaction pushes out the electrons from the negative electrode of the battery, while the reduction reaction absorbs them at the positive electrode. Dry batteries do not have the characteristic of recharging for users and are disposable batteries.

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