Chosen Solution
It may be a bad U2 IC but honestly, would you really expect anyone to go through a tedious “remove and test” for free and why exactly , that’s at least a couple hours time and personally I’d use them on going to the sea or enjoying friends and family or simply do some productive work. You may try and see if you got someone in your area working on a no fix no fee basis but if fixed that’s going to cost you. Battery at 3.9v. is fine and should be able to start your phone.
