All capsule lights have a micro-USB jack on the side.
Simply plug a micro-usb cable into your capsule light (see micro-usb charging port in picture below) and make sure your cable is plugged into a power source - your capsule light should light up it's charge indicator:
Red = really low, less than 10% left
Orange = okay, about 50% left
Yellow = should last a while, 50-90%
Green = good to go! 90% or more
Blue = deeply discharged, please charge overnight!
