Yes, I've encountered this recently. I once had the phone shut down with 53% battery remaining.
I'm attempting to "recondition". When it shut down at 16% the Friday night, I did a hard reset on it - power button+home button - and then let it go till it shut off again with 12% and did the hard reset then let it get down to 5%. At that point, I plugged it in and charged it overnight and hard reset it in the morning before unplugging it.
On Saturday, I let it go and it "drained" pretty quickly throughout the day, using it intermittently, until it hit 2%. I left the screen on and did other things for 1/2 an hour and came back and the phone was still reading 2%. I turned on the flashlight and started streaming a video through YouTube (two things I've read that help drain a battery quicker) and left the screen on and after half an hour at 1%, the phone finally shut down. Recharged it fully overnight.
It seemed like the phone drained at a normal rate on Sunday, and I used it until it shut down on its own and recharged it overnight. However, this morning, Monday, the phone drained from 100% to 2% from the time I got up (6 a.m.) to the time I got into work (9 a.m.) I played a couple of games this morning, used it to stream radio, road map app and surf the web, nothing terribly strenuous and things I do every morning. I now have had the flashlight on and a video streaming with the screen on - it's been an hour and the phone still reads 2% battery charge!
Update: a few minutes after I posted this, the phone finally dropped to 1% battery charge. Still streaming the video and have the flashlight on.
