$3 USB Li+ Battery Charger

The $3 Li+ battery charger is very simple in construction.  It has a single layer PCB.  I could not identify the IC, which linearly regulates the voltage and the current from the USB 5V input.   It also controls two LEDs, so it may be designed for this application.  One 2K resistor is possibly for programming the current. It draws about 5mA when idle and 500mA when charging.  It cuts off at the right voltage of 4.2V.  But the open circuit voltage is 4.38V.  The negative battery terminal tab is spring loaded to accommodate different battery sizes.