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It's hard to say if there is a fault or not. You can take a look at the following FAQ topic to see if you can find some tips:
http://talk.sonymobile.com/t5/FAQ/Battery-time-and-enhancement-features/m-p/347874
Also, it would be great if you can provide us with some screenshots on your battery usage when you have around 10% battery. You can find the battery usage if you go to Settings > Power management > Battery usage.
If you use data all the time,it will drain your battery fast.Also,sync and games for a long time can drain also very fast.
Post the battery graph and apps on the draining list and we will see.
Do you know how to make a screenshot?To insert an image,you need to use the desktop version of the site,not the mobile.