I heard they had problems with cross threading when screwing on the cap for the battery and it would basically ruin the laser.
I read that in some reviews on Amazon. It seems that by sitting the cover onto the threads and turning left until it "drops" avoids that issue. Once it drops you turn it right and tighten. I'm thinking of getting one since I could switch it between my Glock and AR if I want to. All the reviews I've read about Viridian say that they stand behind their product and will replace any malfunctioned parts.