Adafruit Micro Lipo w/MicroUSB LiIon/LiPoly

This small lipo charger is so handy that you can keep it on your desk or easily incorporate it into any project. Simply connect it to a USB port using any MicroUSB cable and attach a 3.7V/4.2V lithium-polymer or lithium-ion battery to the JST connector on the other end. There are two LEDs - one red and one green. During the charging process, the red LED lights up. When the battery is fully charged and ready for use, the green LED turns on. Seriously, it doesn't get any easier than this.

Charging occurs in three stages: first, a pre-conditioning charge, then a constant current fast charge, and finally a constant voltage trickle charge to keep the battery topped off. The default charging current is 100 mA, making it compatible with any battery size and USB port. If you prefer, you can easily switch it to the 500 mA mode by closing the jumper on the front if you only want to charge batteries with a capacity of 500 mAh or larger.