So i have a replacement Iphone 5 thats is still under warranty and didnt know what to do. its been perfect for a month or two and this morning the battery drops to 86% after 3 minutes of use. so turned it off and back on. it drops two more percent. so i reboot it ( hold down home and sleep button). it starts dropping more. so i plugged it back in. its charging rather fast also. I dont know what to do. Do i just use and run it down to 0%? do i reset it? do i plug into itunes? also, is this a sign of a bad battery. i could get replaced or is it just a glitch and will go back to normal. I was getting between 7-9 hrs depending on what i was doing before. Just really lost on what i should do.