When do you change the iPad battery?
I have owned my iPad since April of last year and I use it every single day, every day, for wrtiting documents, reading books, playing games, listening to the radio, watching video, etc. The battery is fine, though on days when I use it many hours it discharges to 50% and I charge it. I do charge it practically every day, but that has been so since I got it. The reason of this question is that I'm anxious one day it will fail when I'm not close to an Apple store. Any idea how long the batteries last? How much they cost? What is a performance sign it must be changed? Thanks.
MacBook4.1, Mac OS X (10.5.8)