Steve this might be of interest to you http://weightweenies.starbike.com/fo...p?f=10&t=88106 It's a very detailed and informative account of building and setting up and bike with Di2.

And spare batteries are soon going to be a thing of the past. Custom builders are already doing internal batteries with USB charge ports built into to the frame!
http://weightweenies.starbike.com/fo...p?f=10&t=79009 Very tech. Even the Di2 control module for set up is being housed in a custom built stem and not hanging around like it does on most bikes.