I started listening to my iPhone's iPod tonight around 12:30 so I wouldn't wake my roommate as I was studying and the battery was at 50% or so, and I just looked at the phone and it's at less than 10%. I've always wondered about my battery not really being up to par, but is this cause for concern? Should I be making a trip by the Apple store and ask them? I've already gotten it replaced once for subpar performance.