I'm about to push the "go" button with Competitive Cyclist for an upgrade kit to try it on my new SL4 Expert. Too many of these "it's so awesome I can't stand it" reports to ignore. Just can't decide on whether to try to get the Specialized bracket for the battery mount under the BB, or set it up conventional, and switch to a seatpost battery when they're available. Specialized has the tech document out on the seatpost battery, which makes it a DIY possibility. LBS previously told me they send frames to Calfee to get fitted for internal batteries. Wasn't too keen on that idea