Thanks, Interesting points about the battery and the firmware.
I mainly use the EN-EL15c that came with the body. If that's charging or whatever I'll temporarily use a EN-EL15 spare, originally from my D750 or D500. I have not noticed any failures related to those batteries but I haven't been...
Removing and resetting the battery resolves the problem. Sometimes it will reoccur shortly thereafter, other times not. This is random and not reproducible. I haven't found any set of circumstances where it happens. I purchased the z8 in December of 23 and the first time it occurred was in June...