On a whim, I opened up the Tickr today--two days after putting in a new battery--to find this:
Clearly there is some condensation getting inside, but even with that, would that be enough to cause the brown...whatever that is...to come out? I can't really tell if it is coming from inside the battery or not, honestly, but not sure where else it would come from.
Cleaned it, put the battery back in, and it still works. But will just ave to order a new heart rate monitor.