Well, I have not had it long enough to get a really good idea of the batteries performance, but after a week I can tell you that the battery life on this thing is fantastic.
With my old Nano, I would listen for 8 hours at work and my meter would be in the red. Now after 8 hours, my meter is barely halfway down. I've even gone two days without charging it without a problem. I could never have done that in the past.