I posted this previously but will post again because I think it will help. If you try it, please post the results either way. This worked for me on another Android device, and it cured my battery issues that occurred after a software update.
A. Clear cache partition. Note, this is NOT the same as merely clearing the cache in your settings menu.
B. Power the phone off.
C. Plug into a wall charger and charge until 100%, then leave on teh charger, powered off, for several hours, preferably overnight.
The above steps will calibrate the battery meter in the phone. It should be performed any time battery levels start to fluctuate rapidly, especially after a software update. The clear cache partition does not wipe out your files like a factory reset does.
Hope this helps... it cured my supposed battery problems twice after software updates.