How many times has the battery been recharged and have you ever let it drain to 0% so it automatically shutdown and then recharged it to 100% before using it? The Battery Guru applications is handy for monitoring battery charge, battery health, number of recharges, and a few other metrics.
It doesn't hurt to do it once in awhile. To reset the battery % it needs to be done. When I first got mine months ago it would run for hours on 0% so I did this and it is a lot more accurate now.