Hi!
To measure the voltage level of a coin cell CR2450 can be done in different ways. You can use the comparator, the low power comparator or the ADC. I wonder which one is the most adequate to use and affects least the current consumption? The CR2450 is the only power supplay in the system and the voltage is 3,0V when it has full capacity and 2,0V when it's discharged.
BR, Nixon