I was staring at your post vaguely this afternoon, when I read “To be honest, I don’t know if I still need try to connect the power supply as well, if he responds just to usb.But i can give it a try”
I never new that the RB would power up through the USB connection! I just tried it now on my RB mock up and yes you can access the file system. It doesn’t look as though it boots up as the led goes green then goes red and stays red.
While you might be able to perform maintenance through the usb without the battery, without a power supply it will not boot, that’s my two cents worth!
I’m no expert and I’m going to continue to test on a more sophisticated mock up.