I cannot explain it, but here it is
1) Yesterday noon, I noticed that battery indicator shows 3/4 of charge
2) Yesterday evening and today morning it shows full charge
3) I have not charged the reader
If I were Sony, I would add some "piezo charger" under page turns button. So while happy user is flipping pages - Reader gets charged
To Sony: Umm, if you decided to do that, don't forget who came up with the idea, ok? I don't need much, just every new gadget you release ... for free of cause