Stuck in reboot, 4013, won't restore

Someone else replaced the battery two months ago before we bought the iphone 6, last Friday my gf took her phone but it wouldn’t power on anymore. It would only power on in the 3amp wall socket, but then it reboots every four seconds. So we placed it in iTunes mode for charging. Connected it to the laptop after few hours, but while restoring we would get an error 9.

Probably something wrong with the battery, lifted the screen and saw that there was missing a screw of the battery/dock connector holder, the battery connector was not completely clicked in *yells*.

Now the phone will show its apple logo without a charger, but still restarts after a few seconds. Back to iTunes mode and left it for a couple of hours to charge. After exiting recovery mode (Reiboot Pro) it still keeps rebooting.

Next step; Restoring in DFU mode. Normally when the firm/software package is unpacked, it shows waiting for iPhone, it then disconnects , changing the mode in the iPhone and then goes further with updating/restoring, but now it disconnects, change the mode in the iPhone (i think) and then disconnects again, leaving an error.

First had 4005 but after replacing the dock connector and battery and leaving the screen off it changed to 4013.

What else can I do?

The battery and dock connector where bought at the shop where I always buy my (i)phone parts. Never had problems with parts except delivery damages. Used also different computers and cables, Macbook and latops.