Thanks for all the tips.
I carried out a digitizer replacement. The Flex cable was lost. I tried a rev1.1 which didnt work, then I used another flex cable from a spare S4 I9505 which no longer works. I got all the buttons working, but as the buttons started working, the phone would get a low temperature warning when charging. I got WD-40 Specialist fast drying contact cleaner, which is normally used for car's electrical connections for cleaning them. I sprayed the port, the flex cable circuit board, the battery metal connection points, and the phones battery connection points. I let them try, then blasted them for about 10 seconds with a heat gun to dry it all off. Put the battery back in and the charger worked! No low temp errors.
Any electrical contact cleaner will work.