MarkT:
You have connected all the unused pins to ground as indicated in the datasheet?Floating inputs are classic way to cause a micro-power CMOS circuit to consume
4 or 5 orders of magnitude more current from the supply than they are meant to.Don't leave CMOS inputs floating.
Thank you for the advice. There seems to be some disagreement in the thread about the importance of grounding the unused pins on the DS3231M.
In the "Pin Description" section of the datasheet, it says of the 32kHz pin "It may be left open if not used", and of the INT/SQW pin "If not used, this pin can be left unconnected". These two pins have pullup resistors in the "Typical Operating Circuit" on page 1, and the RST pin has an internal 50kOhm pullup resistor. I believe that the Chronodot leaves these pins floating. And just to be clear, I'm using the 8-pin version of the DS3231, which has no extra "NC" pins that need grounding.
I raise these points not to be contrary, just be clear. I just checked the circuit this morning and the coin cell battery is at 0.8V, as good as dead. Thank you all for posting, and I would welcome any additional advice.