Under normal reading conditions I find that battery drain is rather fast. I'm guessing here but I think I've read about 5 or 6 hours on my PW2 and it has drained half of the battery. I've only added 3 books to it so indexing shouldn't have been exhaustive, and I fully charged it before using it. I keep the light on from between 7 and 14 with 12 probably the level it is at most of the time. I do run WiFi continuously, but I've always done that on all my Kindles. I think the light is sucking the battery down rapidly. In my case it isn't that big of an issue as I can charge it up each night, but it might be for some people who travel a lot.

EDIT: Amazon claims, "A single charge can last up to eight weeks (based on a half hour of reading per day with wireless off and the light setting at ten)..." That equals 28 hours at light level 10 with WiFi off. WiFi has never been a huge drain on any non-lighted Kindle I've owned, so I think the light is the culprit.