I suspect the reason that the thermostat is reading "LO" is not because of the thermostat, but because of the battery itself. When a small battery like that gets very cold.....it don't work so great. I have experience same situation and when I warmed up the battery, it worked as expected.
Chris
Could be but I think in this case its actually the thermostat. The battery was brand new, it only took a minute or less to warm the thermostat back to a reading (where as batteries take a bit longer) and those same batteries are still working 6mo later.