I would check out the troubleshooting steps in the following article, specifically concentrating on the "Battery life appears short" section:
Thanks for your suggestions, but the only application on was the pedometer, which I never want off. Music was off, also radio, and no podcasts were playing. This is the 2nd time this has happened, battery dying after 6 hours of nothing on but the pedometer. In both cases, I wanted to walk in the hills after work, so maybe elevation was a factor? However, I walk in the hills most days.