I seem to be having the same problem on my Lumia 710. Battery life has been reduced by about 5-15%. Previously my phone could last 6am-9pm, now it can barely get to 7pm
The Windows Phone OS has always had trouble keeping valid, accurate statistics to battery, leading to less-than-sufficient power available to your device. This is caused by a single file within the phone called records.dat the OS uses to predict how much power is left and how long till it needs to charge, based on previous battery usage and consumption stats. You can delete/rename the records.dat file in /Application Data/Microsoft/BATSVC to reset the battery stats, assuming your device has full root or interop unlock, power off the phone and take the battery out, reassemble the device and power it on. (You may need to press and hold each hardware key about 20 seconds when the battery is removed to ensure no electricity is leftover. Otherwise, stats are likely to be inaccurate.)
Other than that, the only way is to hard-reset your device, since that method ALSO resets battery stats, but not everyone is too keen on reinstalling apps and games, as well as photos, music and videos, in exchange for longer battery life.