I can’t find an active thinkpad centric community on here I am just going to post here. My Thinkpad T480s, 16 GB RAM, 238 GB SSD is randomly shutting off while at like 50%. When I try to open it back up it always is dead and I have to connect charger to boot it up again. Why is this happening? Is it battery issue? It complains about not being able to read temp2_input while shutting down and sometimes say PM usage count underflow. Not sure what that is supposed to mean.
Oh, wait. 50% and Thinkpad. I used to have a Thinkpad with two batteries.
https://www.ifixit.com/Guide/Lenovo+ThinkPad+T470S+Batteries+Replacement/140443
That looks like the T470s has a dual battery, and unlike mine, they look like they’re the same size. Does your T480s have dual batteries?
EDIT: The T480 apparently does. Does the T480s?
https://www.reddit.com/r/thinkpad/comments/a4iben/t480_confused_on_how_to_charge_2nd_battery/
EDIT2: I don’t see anything that looks like a second battery myself in this:
https://www.ifixit.com/Guide/Lenovo+ThinkPad+T480s+Battery+Replacement/144009
So I’m guessing not.
Still, a promising lead. I hope OP comes back with an answer. My money is on the battery, one way or another.