It's 2013, and bicycles are finally entering the space which has up 'til now been occupied mostly by high-end electronics: the "slimmer, lighter model this year" arena. Yes, now that our bikes require batteries to shift (thank you, ShimaNO and Campagnolo), we have the need for ever-smaller and -slimmer batteries (think about every year's refresh of the iPhone). Because nobody wants a heavy battery weighing down their electronic bicycle.
If only someone would invent a shifting system that didn't need batteries. Oh, wait! We've had that for more than 100 years!
Here's the link for more info: Campagnolo offers streamlined EPS battery | Bicycle Retailer and Industry News