I fear that the battery on my IPhone 4 is starting to fail. I always charge my phone at night before I go to bed. It's always at 100% battery life when I go off to sleep. And when I get up the next morning it usually still at 100%, or at the worst it's around 98%. But the last few days my battery life drops around 85-87% by the time I wake up the next morning. Is this the beginning of the end for my battery? What options do I have about fixing or replacing if it continues to decline?