Backup data from the RTC when the main power is cut off

[VOliv.5]

Hello everyone, I'm using RTC on board NUCLEO-L053R8, so I have some problems. How do I connect a battery in this board? I know that if I want save my battery lifetime I have to put my microcontroler in a mode as StopMode, but how can I do that when my main power cut off and use only the battery? Another question how do I send my Time and Data Register from RTC to the Backup Registers while the microcontroler is in StopMode? How do I wake up from the StopMode when my main power supply return?

Sorry it's so much questions in a single topic, but I will be gratefull if anyone can answer them.

[turboscrew]

It looks like you need to solder to put a backup battery. The place seems to be the processor end of SB45.

The RTC doesn't get powered off, if you put the device in low power mode (it belongs to the backup domain). Maybe you don't turn the main power OFF at all - the chip doesn't consume much power in the deepest sleep modes. If you want to turn the main power OFF, then you need to add some trigger circuit and connect that to the WKUP-pin.