Adafruit micro li po usb li ion li poly charger adafruit 1304 p the adafruit micro usb li ion and li poly charger is a must have for any toolbox with a constant 100ma charge current you just plug it into a usb port attach a battery and wait for the green led it is specifically designed for charging the 3 7 4 2v lithium ion or lithium polymer batteries rather than the older 3 6 4 1v batteries it uses a 3 stage process starting with a preconditioning charge then a constant current f