Neverending reboot after battery replace

Hi everyone, since my 4S was totally out of charge (it was lasting 3hrs...), I decided to buy the ifixit kit and change it myself.

The guide is perfect and the job is easy and quick.

But after the first reboot, I got a couple of problems.

First one was the not working network ... well no problem..hard reset and perfectly working...but I suddenly found another bad problem...the screen, in a random time (no more then 2/3 minutes), fade out and the phone reboot. And it reboots and reboots...everytime that it starts, I see a different battery percentage.

I tried a DFU restore, but the phone reboots too early and it cant be completed (maybe even started).

Any clue?

Tonight i'll try to reinstall the battery and see is something went wrong..but I checked yesterday already and everything seemed okay.

thanks for your help

Claudio