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I agree with @Phy, the graph show that the WiFi its on all the time, that will drain quite a bit of your battery
Indeed that doesn't look normal, what I would do is to repair the phone with PCC
software repair using PC Companion
it could be a bug or it could be an app acting up
Bridge (for Mac)
Alternatives on How to backup Xperias
Only your Local support could answer that question after they have inspected the phone.