OK, M92 was in low energy state (battery crossed). Maybe at this state the pen is turned off, while buttons not to enable user to finish the work and switch device off. So, nothing strange has happened to you.
Difference between sleep mode and off-mode is, that in sleep mode some energy is used. In off-mode almost none.
Try the charging again. It takes (IMO) few charging cycles before any recharcheable battery reaches its full capacity. To say the truth, I do not know, how often m92 needs to be charged. There is so many hungry devices, that I lost the track...
I charge it when needed.