Chosen Solution
i have 2 iphone 4. one is locked to some network and second I bought cheap because it have broken screen. i test it both and both of them charged very fast. than I put logic board from broken iphone to locked and than i normally turn on iphone and everything works normally but when i connect charger cames icon for charging but batery pecentage became lower and lower. can it maybe be because I didnt put all screws. and why are input to motherboard 5 V and port for batery have 1.2 V. now i check again now it is 0.4 v? any help?
Because you damaged something in the charging circuit—first rule out parts. Follow an iFixit guide to remove the charge port from the other phone, without installing it fully, just overlay and click into place, see if that port will charge this phone. If not, then you have ruled out parts. (FYI, screws are not important for this problem). If your problem is the motherboard then you have likely knocked off some very tiny components near the battery connector or near the dock connector on the board from disconnecting the battery/port—use your fingernail, not any tools.
