Just a follow up. Eventually it was the middle pin which was the battery presence one. I wired a resistor there and it was able to boot up. But i had some problems supplying enough current to it. It was simply so thirsty :) Eventually 1A works. Also, i spent some time designing and printing the plastic block to fit in but the first idea was not working. It was killing all the thiny buck converters that i had. So i got some pretty strong DC-DC power supply and converter, set it to 3.8V and now it’s working fine.
