I have a homemade clock based on an atmega328 and a DS1307 Real Time Clock. When off, the DS1307 is powered by a 3V CR2032 coin cell, as usual.
If I leave the clock off most of the time, how long should I expect the coin cell to last?
I'm aware of the formulas for calculating the battery discharge time, but I'm probably failing at applying them right (I think). According to my calculations, it should last approximately 50 years based on 210mAh capacity of the battery and 500nA of current draw from the datasheet. But the current draw is so low that there must be other issues dominating the battery discharge rate.
So, does anyone have any better figures than I have? Any real experience? Did anyone's battery die before 10 years?