Well, replaced the battery, we'll see how it does in the morning. Pulled a piece of crap out of the rain gauge while I was up there.
It did this once before not too long ago. The thing that threw me was that WD was still showing activity with those little flashing green lights. It appeared everything was ok. But once I saw a graph of my data, I knew it wasn't working. And also, the much cooler temperatures probably exacerbate the effects of the supercap going bad.
If it is the battery, I have no idea how long it might have been bad though. Does the console tell you if the ISS batteries are going bad or is it just the console batteries it tells you about ? I can't find it anywhere in the manual except for the console.
Battery Replaced - 10/22/11 Let's see how long it last!