I have the same problem as well, tablet blackout with detach button red light on, and the tablet is not able to charge even I detached it from the keyboard.
Right now I am using a tape with a memo to stick down the power and + volume button as I don’t know how long it takes to get to the UEFI menu come out. I’ll just wait till I see it or wait another week to let the battery flat out.
To detach the tablet, 6th ventilation hole from both side and insert in adjacent angle for about 1 inch then you’ll hit the click to detach. Tricky part is to hold one side detach while fixing the other side, which makes it very easy to attach again…