Is STM32L412CB can get damage when, On Vbat pin, the Coin Cell is inserted with wrong polarity(by mistake), for 2-3 seconds.

[DBhut.1]

..

[AScha.3]

unpowered cpu, i suppose .

+ wrong polarity -> cell current going through (protection) back diodes on chip ->

depends on cell (age and source resistance) how much current cell will deliver,

with "new and good" CR2032 have good chance to kill the cpu (or at least some part of RTC circuit);

with an old and almost empty cell i tried this myself, nothing was damaged.

if this has to be avoided, you could use a shottky diode invers parallel to the cell, so in case of wrong polarity the cell current would go thoug this diode and protect the cpu.

btw

if using this type of batt. holder , reverse position -> nothing damaged. (because no contact to neg. polarity side of cell);

so if using this type of cell holder, nothing can be damaged with wrong inserted cell !