The hibernation module can be independently powered by a battery or an auxiliary power source. The module can monitor the voltage level of the battery and can detect when the voltage drops below VLOWBAT threshold. The voltage threshold can be between 1.9 to 2.5 V, and is configured using VBAT select field in the hibernation control select register. Battery voltage is monitored while in hibernation and the microcontroller can be configured to wake from hibernation if the battery voltage goes below the threshold. The hibernation module can also be configured such that the device does not enter hibernation when the battery voltage falls below the certain threshold. It is important to make sure that VDD is higher than VBATT or the hibernation module will draw power from the external battery and it will be drained.