I don't think fanuc use RTC clock so it's normal. Use NTP<
I have seen almost all robots go wrong by a few minutes after several months/years...
Yes, most robot internal clocks are no more accurate than a PC motherboard clock (often the same hardware, in fact). On PCs, it's usually not noticed b/c most PCs are on the internet and update their clocks to an NTP server regularly.
The times I had to have all robot&PLC clocks set accurately, the customer had to have everything air-gapped, so we ended up building a local NTP server on the line serving all the automation, and the custmer had a highly-secured facility-level NTP server which would update our "local" NTP server.
