It is worth remembering that 3.0V lithium batteries are supported. When Axel Lite enters RTC mode and 3V3VIN voltage is removed, current absorption from PMIC_LICELL pin is about 135uA. This value is relatively high with respect to the typical lithium coin cell battery capacity (10 - 50mAh) that may not satisfy RTC keep alive time requirement. In this case, please consider the use of an external low-power RTC device.