This Lithium Ion battery charging module is ideal for charging a single cell 3.7V lithium cells such as 18650s.  This module is based around the TP4056 integrated circuit (IC) and DW01 IC.  This Li-Ion batter charger module can be used for charging 18650, Li-Ion, Li-Polymer and other lithium batteries.  This module charges at 1 Amp current and then switches to constant voltage charging mode when approaching the cut off voltage of 4.2V.  This unit includes protection circuitry so it is more than a simple Li-Ion charger.  During discharge, if the battery voltage drops below 2.4V the protection IC will disconnect the load from the battery and protect the battery from damage.