Lithium
I'm going to have to disagree about the E+ Lithium. I bought the E+ Lithium Battery and it lasted about 5-6 months. It was nice to have the extra range for the time that it worked, but it was a complete disappointment from a value perspective.
YOu might notice that they no longer sell the lithium battery on their site. I suspect that's for good reason. Hopefully they'll come up with a better "2nd battery" solution soon. In the meantime, my original Nickel battery is working just fine, though I do miss the luxury of having twice the range that 2 batteries affords you. I also miss the money lost on the Lithium. The lithium was only warrantied for 3 months. So I was literally out a grand, and though to this day I love the bike and the nickel battery, I felt scammed by the whole lithium debacle.