There can be a huge impact on IBAK when disconnecting and reconnecting the RTC backup power source (battery or Supercap) without main (VCC) power is ON. When the nvSRAM RTC device switches from the main power to the backup power, it internally switches the RTC circuit configuration from HPM (High Power Mode) to LPM (Low Power Mode) to ensure that the oscillation continues with minimum circuitry ON to keep IBAK minimum( you will observe this value within the datasheet specifications). When the battery is removed in LPM, the device LPM configuration is lost and when the battery is reconnected, the RTC circuit starts getting the power supply, but the state of the circuit remains unknown and it can be LPM, HPM or any other undefined state. Any state other than LPM will draw more IBAK current.
Thanks and Regards,