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Shimano's Dura-Ace Di2 takes shifting to the next level. The Rear Wiring Kit connects to both the left and right shifters and Junction Box A (which displays battery power and allows manual adjusting). It also includes a battery mount, cable covers to route and hide the cables and a wire plug/unplug tool. The External Kit is meant to be run on the outside of the frame.

Campagnolo's Record EPS V2 Interface Unit is like a translator, the vital piece of the electronic shifting puzzle. Mounted to the brake cable or the handlebar, it processes the data churned out by the EPS Power Unit (sold separately) and communicates it to you via an easy-to-read colored LED. Plus, it plays the critical role of converting every analog shift you send its way into a digital format so the system can work as a cohesive whole. There's also an easy-to-read LED battery gauge so you know when it's time to recharge the system. And don't mind the weather, as it's totally waterproof.