This is a charger for lithium ion batteries which takes its power from the USB port of a computer.
It uses the MCP73861 or MCP73863 Li-ion battery charger chip manufactured by Microchip.
Microchip MCP73861 or MCP73863 are advanced, fully-integrated, single-cell Li-Ion/Li-Polymer charge-management devices allow these peripherals to utilize the full power of the USB port.
Li-ion batteries come in various flavours - single cell, double cell, coke anode, graphite anode etc. Each has to be charged to a specific voltage. Too low voltage leads to undercharging, with the result that the full capacity of the battery is not utilised.
Over charging the battery, even by as little as 0.1V, can lead to "spontaneous disassembly" of the battery, according to one manufacturer. That means it can explode, and catch fire, and potentially cause personal injury.
Use this circuit at your own risk.
The datasheets of the chip give information on configuring the chip to cope with different types of battery, and is an essential document in using the chip.