C stands for a chemical battery with lithium metal as the negative electrode and manganese dioxide as the positive electrode, and R stands for the cylindrical shape of the battery. The first two digits of 20mm represent the battery diameter, and the last two digits of 3.2mm represent the battery thickness.
Button battery, also known as button battery, refers to a battery with an external size like a small button. Generally speaking, its diameter is larger and its thickness is thinner (compared with cylindrical batteries, such as No.5 AA battery on the market). Button cell classifies batteries according to their appearance, and the equivalent batteries are divided into columnar batteries, square batteries and irregular batteries.