I recently found out I can drain my battery in a few hours if I have WiFi on, so I only switch it on when I'm synchronising/downloading books when using the computer is not an option. Saying that, the battery usually jumps level usually jumps up a few tens of a percent when I switch the WiFi off, so the battery indicator probably isn't accurate under high usage.
Aside from that, the battery seems near infinite, and I'm really picky when it comes to advertised specs not being fulfilled. At the moment I'm reading The Idiot, a long piece of Russian literature that, if it were a hardcopy, could be used to bludgeon someone to death. I'm around half way through the book and approximately half of my reading time has been with the light on (lowest setting). The reader was charged before I started and now the battery is at 94%, so it's holding up well. With my font settings, that equates to 600 page turns, or about 10,000 turns if the battery indicator is accurate. That's stunning, considering the light has been on for a fair amount of those turns.
It definitely took a couple of charge cycles for it to start performing like that - the first week I had to charge it way too often, but I was only putting the reader to sleep, so perhaps that was the issue. Now I turn it off completely, turning it on only once a day for a couple of hours of reading.