Ian Austen for the New York Times:
Shimano’s version, known as the Dura-Ace Di2 7970, is being used by three professional teams competing in California: Columbia High Road, Garmin Slipstream and Rabobank. About 10 riders will race with the system even though they have used it on only one or two training rides after receiving them late this week. Bob Stapleton, the owner and general manager of Columbia, said many of his riders had doubts about using bicycles that could literally run out of power. The Di2 system has no manual override if its battery goes dead. That event can be an irritation or a disaster, depending on the terrain and what gear ratio the bike is stuck in. Shimano estimates the battery will last for about 1,000 miles per charge.In the Times' story, the above graphic interactively shows how the new system is rigged into a bike.