Denver bought a bunch of electric busses from BYD for service on the 16th street mall. My understanding is BYD offered a 12 year warranty on the batteries, in order to make the economics work.
I proud of my little city for leading the way, but I'm a little sad to see that TransTeq seems to have disappeared. For a while, it seemed like their ideas were taking over the world. But at least the technology advanced overall.
Anyway, my favorite part about the new BYD buses on the Mall is their noise. They have a speaker on the front that 'growls' so that the otherwise-quiet buses have a harder time sneaking up on pedestrians. New solutions to new problems!