I don't know what kind of battery is used in the Kindles, but batteries of most Tablets, Smartphones etc. need a couple of cycles to reach their full potential. After charging and discharging it a few times, battery life should get a bit better.
Since receiving mine 5 days ago I have read on it every day for maybe 2 hours, with light on 11 and wifi off and the battery is still at about 80%. I'm really happy with it but I have only used tablets and smartphones to read my ebooks on lately so every gadget that lasts longer than 2 days with a charge feels great to me.
