Off the phone while it's been charging. Leave it at charge full night. When you wake up in the morning, on the phone while it's still charging, once it finish booting up completely, perform a hard reset (push down home and power buttons at the same time until the screen goes black and comes back on with the white apple logo, then you release both keys) after the phone boot up, wait 1mn, unplug the charger, wait 1mn and plug it back, go to settings> general> usage/ if the usage time shows - then unplug and plug back the charger, if the usage time shows 0 then make sure that you have the FULL CHARGE icon in the battery, not the thunder icon.
After seeing the fully charged icon, and that the usage reading 0 then you can unplug the charger from the phone. Make sure that you don't plug in the USB cable and connect it to a computer during usage time, otherwise usage time will not be valid anymore since the battery is taking charge once you connect it to a computer. Let us know how it works out.