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I originally updated my Z3 to the latest software version due to rapid draining of the battery (I'm talking full to flat within 10 minutes). It half solved the issue, making the battery life last a bit longer. However, it also created new issues. I get constant popups saying that the capacity for NFC services is full, however it will not show me any of these services if I try to disable them. The phone often crashes after receiving these messages and will display 3% or 4% battery message. If I switch the phone back on, it's normally at the percent that it was on when it crashed as opposed to the 3 or 4. I have no banking apps on the phone.
you should repair the phone with Xperia Companion and see if that solve the NFC issue, as for the battery, you might need a new one as the phone it's quite old