I started out the cold commute w/o my battery adapter cable. That meant no rear dionette. My backup was an old lollipop style cateye dangling from my camelback.
At a light the lady in the next lane called out that the cateye was dim & she had only seen me by my bright headights. A very nice contrast to the occasional honk or shout! I promptly cranked my DIY halogens to full power. About a mile away from home the battery circuit cut out leaving me in the dark.
It was one of those "I'm getting tired of this winter commuting" commutes - but at least the comment was a bright spot.