From a datalogger hanging on a string in the well pit, about three feet underground, in December:
The temperatures continue downward in January:
The corresponding attic air temperature record for January ends early:
When the air temperature dropped to +11 °F in the early hours of 17 January 2015, the well pit hit 35.5 °F. It was just over 35 °F in the wee hours of 29 January 2015, but the attic logger gave up as the battery voltage declined to 2.8 V.
Evidently, the new Maxell CR2032 lithium cells don’t do well in extreme cold. They’re rated to -20 °C = -4 °F, but that spec applies for a very low load that surely doesn’t include blinking a red LED.
I’ll take a look at that logger in a few days, then hack a pair of AA cells on the back if it’s dead again. Alkaline cells aren’t very good in cold weather, either, but they may have a better minimum voltage.
Or it’s just another batch of dud CR2032 cells…