Lithium batteries are rechargeable batteries of 3.7V. Lithium batteries offers one of the highest energy density. Due to this, Lithium Ion packs are most compact. Lithium packs should always be assembled with suitable battery protection circuit. Without suitable BPC, the pack could have short life. In addition, it could also be unsafe. Lithium batteries are available in Cylindrical shape and Prismatic shape. These are available in capacity range of 300 mAH to 4 AH. Cylindrical batteries are available in dimensions known as 18650, 18500, 14500, etc. The first two digit reflect diameter of cell in mm. The next two reflect the height of cell in mm. The last digit would be used to further characterize the cell. Special range of Lithium cells are available for High Power applications such as portable tools. Prismatic Cells are available in large variety of dimensions and capacities.