My attempt to recalibrate the battery on my X220 failed. Hunting for info I found this on github
It's a TLP bug that was fixed a couple of weeks ago. The solution was to install the git versions of tlp.
yay -S tlp-git tlp-rdw-git
Now I can plug in my X220 to the mains and run tlp recalibrate BAT0 overnight.
ยง