Barchettaman beat me to it, but here is the one I use for all my older machines with no dyno at night.



Made by EverReady (who also made batteries), probably 1970s this one.
I use 2x rechargable R2 D batteries and it works fine and will fit all bicycles with that type of bracket. (Most)
The rear view explains the fixing.
Works well enough for me and one charge gives 6/7 hours of usage.