SAFFETY WARNING TAIL LIGHT-As a bicycle safety warning light,20lumens output is enough,it is bright, compact, easy to carry, and most importantly, not expensive, very worth buying USB RECHARGEABLE AND SAVE YOUR MONEY - Never Waste Your Money on Batteries again! Save the Hassle to Replace Batteries Every Week! They charge from your computer or any device with a USB port. Takes 2-3 hours to fully charge and has a Runtime of 4-10 hours on the highest setting EASY TO INSTALL AND REMOVE - Leave your screwdrivers in the toolbox, and detaches in under 2 seconds with NO tools required. Can be mounted almost anywhere. WATERPROOF AND SHOCK RESISTANT:IPX4 Waterproof grade Suitable for the professional or casual bicycle rider.