Use the power saver that comes with the phone to save battery automatically at night (set up Timed Saver) and when battery is about to dry (default 25% battery saver).
Set it to turn off everything during power saving to achieve maximum batt life.
With this on, I only get about 5% power loss in the morning after a full charge the night before.
I think this is a very good feature sony has add to its phones.
Install GO TaskManager, IMO a very well designed task manager app, functionality is great too.
About the screen,
one, don't put on a screen protector, it degrades the quality of the display
it is strong enough to withstand most scratches.
two, backlight is not really necessary during daytime, 50% brightness is very pleasant to view and saves a lot of juice.
Now, I really want to replace the Sony bridge for mac with other software to copy musics movies and other files onto my device.
The Bridge is very buggy, and slow as hell.
I've tried a few apps outside that claims to able to connect devices with MTP mode, but no luck with the Xperia S.