The Lupine Rotlicht (“red light”) is a diminutive go-anywhere tail-light with some nifty features. Made in Germany as with its headlight and headlamp siblings, it is a first class unit whose flexible strap allows it to be easily mounted to a bike frame or seat tube. The battery is integrated LiIon.
Read my review of the Lupine Rotlicht. I’ve been using it for about two months now. Highly recommended.