The other day my screen went white and said I needed to charge the battery, which I didn't believe. So I turned it off, back on and the battery indicated about 75% or so full. Went on reading and a couple of hours later, the same thing happened.
So I charged it up fully and so far it has been fine since. So I'm not sure if the battery indicator is wrong, ie it was nearly on empty but said it was about three-quarters full, or whether it's some other sort of hiccup.