With this you can replace the batteries with high quality ones. http://www.dx.com/p/pannovo-b-c04-water-resistant-4-x-18650-battery-pack-case-for-bike-lamp-black-254957#.VHQNUrR0y-M
I have the Fenix BT-20 and like it. I mostly use it as a daytime be seen light with the blinking mode. You don't have to cycle past it and the unit has memory. I like the idea of using my on high quality batteries.