iPhone 6s reboots every 3 minutes

The phone had a screen and battery replacement in the past and worked fine. Now the phone wont turn on or acknowledge a lightning cable being attached. Replaced the dock flex with a know working one and still nothing. hooking the phone up to dc power and will boot up and stay on 1% and reboot every 2-3 minutes.

now i don’t care too much for the phone as only to have it on long enough to get the data off which is quite a lot as its 128gb.

any solutions greatly appreciated.

btw i have also changed to working good screen, original screen same with batteries and still the same.