The Samurai Smart Tail Light can be mounted under the seat rails or to the back of the seat post. The built in battery will stay charged for 12 to 30 hours of use (constant full bright or flash mode) before recharging is necessary. It removes easily with a twist/snap and is rechargable using a common mini-USB charge connection. 
 
Features:
Light and vibration sensing for day/night operation and auto brake light feature
Three flash modes or constant
Lightweight - 33gm
Waterproof / dustproof - IPX3 rated
3.7V 300mAh integrated battery
64mm x 32mm x 30mm