iPhone 4s Battery Issue

I have the 16g iphone 4s and I have noticed lately that my battery is slipping away, I know that you aren't suppose to leave your phone on the charger once it gets to 100% so I try to charge on the wall during the day and then just turn my phone off at night, well lately I have been unable to do that and now I see when I wake up in the morning that my phone says 100% so I take it off the charger and then it immediately drops to 99% once I unplug it and then gradually goes from there, I have drained my battery so much that it shut itself off thinking that would help but it did not change anything... I did not purchase the additional apple care when I got my iphone so is there any suggestions to something I can do? I have downloaded battery doctor to see if that changes anything, although I am skeptical about a battery app.... I know the end result will probably be me going to the apple store, but if there is something I can do I would like to do that since the closest store to me is over a hour away. Also I even changed the cable that I charge it with, I switched the cable for the one I use for my ipad, that did nothing either.