I want to detect low battery in typical DS1307 circuit with microcontroller.
My first idea is to connect one of low cost comparator inputs to Vbat, another input to 2.0V from some voltage divider powered from 5V and (comparator) output directly to GPIO.
My second idea is to connect microcontroller ADC, maybe thru some voltage follower made with low cost op-amp.
If these ideas are good: should I pick comparator or operational amplifier with low input bias current instead of regular comparator / op amp?
How this is made in computer motherboards where BIOS can detect low battery and batteries last for few years?