My Surface Laptop 2 is having this issue since May 2019. My case is a little different... I left my SL2 plugged in for weeks (without using battery) then one day I turned it off, unplugged it, and turned it back on in an hour, the battery level dropped to
75%. Then I plugged it in, the Surface was actually charging. Once it was charged to 100%, I turned it off, unplugged it and turned it back on in a few hours, the battery was still 100%. I thought the problem was solved, but I was wrong. After being plugged
in for a few weeks, I turned it off, unplugged it, and turned it back on, the battery level dropped to around 75% again. This has happened a few times to me...
So in my case this "dramatic drain" only happens when I leave it plugged in for a long period of time (battery showing 100% before I unplug it). Anyone is experiencing the same issue? I wonder I might have a defective battery that drains too
fast while not using and the Surface Firmware does not detect this drain either so it does not charge the battey when plugged in. But when the computer restarts, it recalculates the battery level and finds out the actual battery level has dropped to 75%...