A lithium ion battery and a charger thereof are provided. The lithium ion battery comprises a shell (1), a locating seat (2), an end cover (3), a battery cell (4), a positive contact (51), a positive plate (52), a negative plate (53), a positive connecting plate (61) and a negative connecting plate (62). The shell (1) is a one-step-molding cylinder with an upper opening. The positive contact (51) extends out from a contact extending hole (11) of the shell (1). A lower end face of the end cover (3) is tightly pressed on the negative plate (53) and the locating seat (2), where the end cover (3) is detachably connected with the upper opening of the shell (1). A cover edge of the end cover (3) cooperates with an end face of the upper opening of the shell (1). The lithium ion battery is conveniently detachable with the charger thereof.