I forgot to post a picture showing the trace to cut to disconnect the INT/SQW pin from the existing pullup resistor on the typical SD-042 module. That's required because that resistor is pulled up to the module's Vcc pin, but with the power off there's no voltage on Vcc, and that connection just messes up the circuit if left in place.
I should also have added that Vcc needs to be applied to the module only when you want to communicate with it over I2C (because SCL and SDA are also pulled up to Vcc). At all other times it can run off the coin cell at about 1.25uA, at which rate it will typically last a couple years.
