Hmmm I don't know. I had a BU-353 on the roof of my truck for about 3 years here in Vegas. Never garaged and rarely in the shade. It's now been sitting on a ledge outside my window in the direct sunlight for the past 2 years...never out of the elements or the heat, and always worked as expected. I'd bet moisture or just a plain manufacturing defect before I'd suspect heat. Likewise for all my radio and wifi gear. Just about 3 years in the truck without a break...and no failures that I could detect.