1) Where does the electricity go that is not used to shift?
Your not shifting all the time, sure there has to be a little bit used to sense when it needs to actually shift, but that shouldn't use up much and there's no battery on board to store any excess unused electricity.
2) How difficult would it be to put a battery charger in the seat?
There is a mention of storing an Apple Ipod in the seat. Apple sold over 100 million of those and is coming out with an phone. Not to mention every other brand cellphone, portable game, personal organizer, GPS, flashlight, laptop, etc. These all contain batteries that need to be recharged. I'd Co-Market the "Lime" with Apple and anyone else that would pick up half the advertising cost and let 3rd parties sell the chargers. A bike that changes colors, recharges your favorite toy and low maintance, How COOL is that!