I don't think I've ever heard anyone complain about that, and I know a good amount of people who use Garmin watches. My own forerunner is still going strong after 5 (I think) years of use, with multiple runs a week for most of that time.

I know someone whose garmin watch refused to charge after a few years, not sure if it was caused by sweat. Mine is starting to get wonky after a few years. I keep worrying I'll plug in some time and it will stop. anec-data is not that reliable of course.