Datasheet

Upload to your Arduino and check the serial console @ 9600 baud. After a few seconds, you'll see the report that the

Arduino noticed this is the first time the DS3231 has been powered up, and will set the time based on the Arduino

sketch.

Unplug your Arduino plus RTC for a few seconds (or minutes, or hours, or weeks) and plug back in.

Next time you run it you won't get the same "RTC lost power" message, instead it will come immediately and let you

know the correct time!