Sony Xperia P — Xperia P Battery draining quickly after updating 4.2.1 .

You need to watch on why your battery is draining fast, what you can do is goto?settings>Battery - check which app is consuming the battery most if it's an application then forcefully close that application but if its the Android OS, screen etc,... then you can't do anything other than waiting for the next update from the vendor as you said you've been updated recently I think there might be some bugs in the Android OS that needs to be taken care by the vendor, I am sure on the next update this might be fixed. I will also suggest try installing some battery saver apps like DuBattery saver and all..... what they do is they stop the battery consumption in the background.