If we use a battery to back up power to the Imp004m RTC via VDD_bat pin, do we need to use the typical 2 diode circuit to ensure no power is drawn from the battery when main 3.3V is present, or does the STM32 inside the imp do that automatically (as is for instance the case with NXPs LPC176x family) ?
STM32 automatically only drains from VBAT when 3V3 is not present.