Usually a phone reset or reinstallation will help restore battery performance. I'd suggest that you do a PC Companion phone repair, this will do a clean installation of the latest firmware and will also wipe your internal memory. You'll need to backup your data before you proceed.
Open PC companion -> Support zone -> Phone/tablet software update -> Repair my phone/tablet (blue link style). Follow the steps given, do not connect your phone until prompted to press volume down while plugging USB cable.
