If the Device is rooted I've would give battery calibration a try, this would certainly improve the performance.
Advanced users who have root access can full charge their phone to max possible capacity, which means charge to 100%, then unplug charger and re-connect it and
better if you wait for 20-30 minutes with charger connected, and then navigate to "/Data/System/" and delete the file "batterystats.bin"
Once done, let the phone drain the whole battery, till it turns off, Then again full charge it without a break.
A couple of such cycle's should certainly help gaining more time from your battery if cells are not out of life.