I had this recently as well. What I did to fix it was to let it die at the 9% and then I plugged it back in and ran the app Battery Doctor while it charged. The app will tell you when you should pull the charger. After I pulled the charger I let it discharge again and it fixed the problem. This was recommended to me and it might take a couple of times for the calibration to resync.
I try to make it a habit to do this every so often, but I forget. :-)
My guess is the calibration is getting screwy when I "over-charge" my phone. I've noticed many times when I charge my phone I'll pull it off the charger and it instantly goes to ~97% (this is probably a built-in feature of the battery where once it hits 100% it will discharge until 95% and then begin trickle charging again).