Sounds like a calibration issue. Have you tried conditioning the battery?
While Li-ion batteries don't have a memory, there is apparently a circuit that needs to be calibrated for the battery meter. Try running your phone down 'til it shuts off and then fully charge it. Do this twice...Once you've done this, it is preferred that you top off the charge as needed. These batteries do not LIKE being fully discharged and it will affect the longevity if you do it regularly.
And Lith-ion batteries #1 enemy is heat. Don't leave them in a hot car. And try to disappate the heat that inevitably develops w/use. I'll take my cover off and massage the battery to transfer some of it into my hand.
Try searching on Google for more tips.