If you still have this issue after trying the above, there is another possible cause—crud in the charging socket on the phone!

I tried the above and other "software related" fixes, and they would only work sporadically. I then took a torch and looked into the charging socket.

Inside, there was a significant build up of fluff and the like. So, using a fine scalpel blade, I removed it all. Now, the charging works perfectly every time I plug it in.

Warning: The blade will need to be very fine in order to fit behind the plastic piece in the middle of the connector. If you use anything too thick, you could break the plastic piece.