Main Features: ?Intelligent design can sense acceleration and deceleration of bicycle ?Never waste your money on batteries again. Built-in 1200mAh Li-ion battery, and its recharging time is about 3.5 hours ? The infrared ray light has high visibility, and its wavelength is 400 - 750nm ? Replaceable backside strap ? Perfect for improving your safety when riding a bicycle in the dark ? It is powered through micro USB interface