Device charging but wont power on.

Hi been trying to fix my redmi note 8 which wont power on. Not sure what the problem is opened it up tryed disconnecting and reconnecting the battery but didnt seem to work. Then check the bat vol which was 3.5 v which is low but the phone has been dead for a while also it is only a single cell battery. Checked the charging voltage on the battery connector with the charger plugged in and got 1.4v which seeemed low and i couldnt find any voltage online so i changed the charging port which hasnt seemed to work.

Any ideas ?

thanks.