Li-Ion (Lithium-Ion) batteries are a type of rechargeable battery. Lithium ion batteries are one of the most common rechargeable batteries in portable electronics. Lithium ion batteries have one of the best energy densities, no memory effect, and a slow loss of charge when not in use, in comparison with other chemistries of rechargeable batteries. Lithium ion batteries are also environmentally safe because there is no free lithium metal. They come in a variety of sizes such as AA, AAA, RCR123A, 18650, 9V, 2032 button cells, and more.