I did a board for a customer, DS1307 wired up just like the datasheet shows: coin cell battery, 32.768 HKz resistor, 4.7K pullups on SCL & SDA, Squarewave out not connected, power from 5V. Nothing unusual, nothing I haven’t done before.
The battery terminal is measuring 0.4V when the board is powered and no battery is installed.
With no battery, the RTC won’t keep time at all, just outputs a static # that I think is all 1s (0xFF).
Circuit is eating 12mm coin cell batteries - going dead in just 24 hours. What could make them get used up like that?