RTC reverts back to last set value when power removed

Why does the internal RTC back to the last value set when power is removed from the device?

For example - I set the time/date to

AT+CCLK=“07/09/21,13:02:00”

and ran it for twenty minutes. I then removed the power. After a while I reapplied power and read the time.

at+cclk?
at+cclk?

+CCLK: “07/09/21,13:02:24”

I can understand the RTC stopping at the time the power was removed but why does it revert back to the last set time???

Because it doesn’t waste flash write cycles every time the RTC ticks or tocks probably.

Interesting. In older versions it went back to a default time (e.g. some time in 1998, which I found in the oldest module we still have in use.)

Best Regards,
Jan