i got the exact same problem for the past months....on my doogee y6 max. The phone needed magic to charge . I had to place it in such a way that the phones weight would apply force to the usb connection and in a certain angle upside down sometimes it would charge. Finally it lost that as well and went dead like a brick.
Send it to a repair store and got it back today actually....
The technician said the following...."i changed the usb .....charged it but it doesn't hold the charge and every few hours to 4 hours max it discharges....Its not the battery since we tested it and the battery seems fine, its not the usb since we changed it, so it must have something to do with the plaquette of the mainboard."
"somehow in a specific part of the mainboard there is an issue that drains the battery and doesn't allow it to fully charge"
Thats what the technicial said.....
Now either the tech shop are a bunch of noobs or my mainboard has an issue as they say.....
The phone came back and i plug it in a barnd new 4 hub usb plug with new usb cables and still charges for 4~6sec then stops.....STILL LOOKING FOR A WAY TO FIX THIS