I just bought a DS3231 breakout (ZS-042), later I found a topic about it having a "circuit" that constantly charge the battery.
Did you also read reply #5 in that topic?
I found no schematic for the ZS-042 breakout board, but most likely the charging is done the same way as with the RTC Tiny DS1307 modules: The charging is not done with 5V from VCC, but with a voltage divider that divides the 5V by using resistors into a 4.2V/0.8V voltage.
This voltage divider will lead to extra power consumption when the Arduino is powered, and the voltage divider will provide a small current for loading the LIR accumulator, but only until a voltage of 4.2 volts is reached.
4.2 volts is the high voltage for a fully loaded LIR cell with a nominal 3.6V rating.
So the LIR is not "constantly charged", but it is only "charged until the cell voltage is 4.2 volts", which is the same as "fully loaded".