Lithium Ion Battery (Li-ion, Lithium Ion Battery): Lithium-ion batteries are widely used because of their light weight, large capacity, and no memory effect. Many digital devices use lithium-ion batteries as power supplies, despite their price is a relatively expensive. Lithium-ion batteries have a high energy density, and their capacity is 1.5 to 2 times that of nickel-hydrogen batteries of the same weight, and has a very low self-discharge rate. In addition, the lithium-ion battery has almost no "memory effect" and does not contain toxic substances, which is also an important reason for its wide application. In addition, please note that the outside of the lithium battery is generally marked with English 4.2V lithiumion battery (lithium battery) or 4.2V lithium secondary battery (lithium secondary battery), 4.2V lithiumion rechargeable battery (charged lithium battery), so when users buy the battery must look at the appearance of the battery block to prevent the cadmium nickel and nickel hydride batteries from being mistaken for lithium batteries because they do not see the battery type.