Backup battery for RTC?

[Angelo904]

Hi, I can’t find in the BOM or project a backup battery for keeping the time when the main battery is dead… am I missing something? How is time kept?
Angelo

[d3mon187]

It won't keep time when the battery is dead. Currently, when it is powered on, the clock will start at 12:00 and count up from there. It does update the time when it receives a notification iirc. It wouldn't be too difficult to add some code to retrieve the time over bluetooth, but I think everyone has moved on from the project, and some parts may not be available. If you still want to try, https://github.com/dannygrob/OpenWatch is the project to attempt. I really enjoyed learning how to build such a device, but it was not easy and my finished product was not something I'd ever actually wear. Good luck! :)

[Angelo904]

It won't keep time when the battery is dead. Currently, when it is powered on, the clock will start at 12:00 and count up from there. It does update the time when it receives a notification iirc. It wouldn't be too difficult to add some code to retrieve the time over bluetooth, but I think everyone has moved on from the project, and some parts may not be available. If you still want to try, https://github.com/dannygrob/OpenWatch is the project to attempt. I really enjoyed learning how to build such a device, but it was not easy and my finished product was not something I'd ever actually wear. Good luck! :)

Thanks a lot for your answer! Actually I am not trying to build that specific device, but a simpler watch without any connectivity.
Since I am a beginner I am having a hard time understanding how time keeping works and why people add crystals or RTC modules (I am not even sure about the difference between the two) to chips (which I believe can keep time on their own) if not for adding a backup battery to store the time when the main battery dies…
Angelo