Since my original posting, my lithium battery has gone bad. It's currently in the shop and being looked at.
As I understand it, they may not be selling additional lithium batteries right now due to a supplier issue. As it was explained to me, the cells are made by a company that was affected by the Japanese earthquake.
In the meantime, my nickel hub battery has worked flawlessly in the 1 year that I've owned it. I do miss the extra battery and freedom it gave me to go further and faster.