Xperia Z5 - E5823 - Bootloop - No Power no

I am currently attempting to bring back to life a customer's Xperia Z5 - E5823 - that was brought to me stating it had a charging problem - either faulty Usb port - or dead battery, although I now think customer might have attempted to flash it with wrong firmware (my supposition)
The battery is definitely dead as the phone does not "power on- or attempt to boot" unless when connected to a power source or computer. Connection to Sony Companion fails to recognise the device and because customer wants me IMPERATIVELY to save data (images and contacts) from internal drive - I cannot carry out a software repair - which will wipe the user data.
I substituted the USB flex - port but not the battery yet as I am still waiting to receive it in the post.
The usb port works perfectly but it is definitely not charging the battery.
While connected to a Mac I have restored the original Firmware (6.1) via Flashtool (avoiding to wipe userdata).
The process completed successfully but the phone would not start anyway. In order to try and retrieve data from it and carry out a complete format I attempted to connect via ADB/fastboot. Fastboot works but ABD, which could allow me to save data, cannot work as the developer mode is not enabled and the bootloader could not be Unlocked as ADB does not respond or allow certain operations.
When the phone attempts to boot the Backlight turns on but boot does not carrying on as normal and no boot splash image or anything comes up on screen. Hardware/soft reset does work but does not do anything.
I disconnected the battery and connected to a power source and the phone/screen kept on flashing. I reconnected the battery after 10 minutes but nothing worked.
I flashed via flash tool the latest 7.0 firmware, without wiping user data: the process completed successfully but phone would not reboot normally.
Th only chance that I have now is replacing the battery in the hope that it will bring the phone back to life.

Has anyone else experienced the same issues? Any advice on how to procede further?

Thank you very much.

 

same problem, still try another methode