Often the I2C master [here, the stm32] is strong enough to force a line to 0V through a 4k7 resistor. I bet the problem here is the RTC itself which should probably have weak output drivers unable to push the lines to zero Volts (thus, very low current drained which is a good point for a RTC in term of power consumption).
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Often the I2C master [here, the stm32] is strong enough to force a line to 0V through a 4k7 resistor. I bet the problem here is the RTC itself which should probably have weak output drivers unable to push the lines to zero Volts (thus, very low current drained which is a good point for a RTC in term of power consumption).