Why does this ThinkPad T440s intermittently refuse to power on?

I press the power button on my ~2015 ThinkPad T440s and there is no effect whatsoever. The problem occurs regardless of whether the A/C adapter is connected and whether the removable battery is present. Moreover, disconnecting then reconnecting the A/C adapter does not cause the power button to flash as normal. The issue has happened twice so far, two weeks apart. Both times, I have solved it temporarily by disconnecting then reconnecting both the CMOS battery and internal backup battery. Then I can boot as normal. Other details that may be relevant: After doing the fix described, I can boot o

Question by fishyfriend on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.