Low battery detection circuit that can tell if temporary voltage dip or actual low battery
What you want is a low pass filter.

A temporary dip is a high frequency event, while a real low battery is a low frequency event. If you pass this signal through a low pass filter, it will remove the high frequency events, and allow the low frequency one to pass.



Increasing the value of the capacitor and resistor increases the time constant, thus decreasing the frequency threshold.