18650 is a standard lithium-ion battery model set by SONY, the originator of lithium-ion batteries, in Japan in order to save costs, where 18 means a diameter of 18mm, 65 means a length of 65mm, and 0 means a cylindrical battery. 18650 theoretical battery life is 1000 cycles. Due to the large capacity of the unit density, most of them are used in laptop batteries. In addition, because the 18650 has a very good stability at work, it is widely used in various electronic fields: often used in high-end strong light flashlights and portable power supply, wireless data transmitter, electric heating warm clothes, shoes, portable instruments, portable lighting equipment, portable printers, industrial instruments, medical instruments, etc. The mainstream capacity of 18650 batteries ranges from 1800mAh to 2600mAh (the capacity of 18650 power batteries is mostly 2200~2600mAh), and the mainstream capacity even has standard 3500 or 4000mAh or more.