This is an illustration of the “textbook” example for charging a Li-Ion cell. The charging profile is referred to as “CCCV,” meaning constant-current, constant-voltage. When the battery is at low voltage, a fixed current is applied to the cell until its voltage reaches 4.2V. At this point, the system switches from constant current to constant voltage mode.The cell voltage is never allowed to exceed 4.2V, which means that the current is gradually reduced until it is nearly zero. When the cell voltage is 4.2V with no current applied, it is considered full. In this drawing, the blue line is the charge current applied. The grey line is the cell voltage, and the red curve represents the total capacity of the cell.