Only twice have I needed a spare headlight which I did not have. Once because I forgot to charge my headlight and it died 1 mile from home. The other is when I dropped my headlight walking out to my bike and it "broke" meaning that the battery connection inside the light came undone. I did not have a small enough allen with me to open it up nor did I even think about that, just thought it broke. Caught a ride home with a co-worker that night. Still to this day just use one head and one taillight for my commutes and late rides.