OK, So the point that the phone just start booting just the moment the battery is inserted got me thinking
IS IT THE POWER SWITCH?
and indeed it's, the power switch is stuck on, although I can feel the click when I push, still, seems like something is wrong with it
so I tried to suck it out, hit the phone softly few times while the power switch is facing the ground
inserted the battery, aaaand, it didn't start booting, pressed the power softly, and horaaaaay, it's working