My Kindle Paperwhite told me the battery was almost empty! It's the first time I saw that dialog, and I haven't actually ever charged it since I have it (december 2012)
Most of the time I connect it to the computer to sideload some books to it, and then I leave it there while still on the computer. That practice has been enough to keep it going for 2,5 years; until now. I forgot to sideload some new books yesterday, so I had to do it in a hurry before work today, or spend a 1,5 hours bus drive back and forth without a book.