Comment 27 for bug 1824886

Looking to comment #20 it looks like a kernel issue, the /sys entry tell the charge level is 100%

Is /sys/class/power_supply/BAT0/status also telling you 'charging' when it's on battery?

Googling a bit I found https://bbs.archlinux.org/viewtopic.php?id=238944 which states it started being buggy on the 4.17 kernel, which would explain why it works on the 'old 4.15' kernel you have with mint.
The comment also state that it's fixed in kernel 4.20.13, could you try on a 19.04 liveCD to see if the new kernel there makes it work for you?