Originally Posted by
degnaw
Never? (sarcasm)
In fact I only use a single taillight (A Cygolite Hotshot), and I've never had it nor my older Superflash go out on me.
I would also recommend a second tail light. I have had the old SuperFlash quit on me without warning and I doubt that the Hotshot is totally immune from sudden failure. There are lots of very inexpensive but quite functional tail lights that provide a valuable backup if your primary light fails. And with a tail light it might be awhile before you notice that it has stopped working.