I just got mine and am still working out the tail light mounting location, but I put the battery where I put the one from my old light, in a seat pack attached to the top of the seat stays between the front of my rack and the seat post. I stuff in the whole Y cable and connections in it then the cable just gets wrapped around the top tube. Easy to take on and off and the seat pack is big enough that I can stuff the whole set up in side if I needed to and take it with me.