One hangs from the rear view mirror in my car, the other I have never taken out of the package. Like bbrins, I have about 4 or 5 of those free ones you get when order something, I usual order from BatteryJunction. Amusing coincidence, I just found 4 key chain lights in the trash bin at my apartment complex, they all work!
Two in total. I have a white LED version that sits mostly unused because it is constantly turning on in my pocket and killing the battery. I gave a blue one to my daughter and it works fine...She named it "Little Blue".