I just wanted to share the picture with you, guys.
The phone lasted for 42 days in airplane mode on single charge, almost without any usage and still 14% left. The experiment was done by my friend here.
I haven't found the guide to unbrick the SE Xperia 2011 "bricked" device, then here it goes.
All of the following worked on my ST15i Xperia Mini Smultron.
So, your device was briked (doesn't turn on and probably blinks its LED).
If your device's LED works or you are able to turn it to...