If you have a rack, it's easy, peasy. Just double-wrap the O-ring around a rack leg.


When I move it temporarily to this bike, I mount it on the outside of the leg.



Ordinarily, it lives on the Portland, where I mount it on the inside of the rack leg so it doesn't interfere with the panniers. It also clears the fender, although it's tough to tell from this angle.



In both cases, I velcro the battery pack to a rack cross-member, shown here on the Portland.

Seatpost mounting are for wussy!