Ni-cad makes my mind wander to the trusty old mag charger and slow trickle charge... I think you could build then into a light with similar properties. I also THINK you can put a fairly high drain on these things. An alwas-plugged-in-charger incan spotlight perhaps? But don't take my word for what you can do with ni-cad, nip over to the battery subforum and aks there.
Whatever you do, please remember that these batteries should be disposed of properly, not tossed in regular garbage. Cadmium is yet another substance you'd want to keep out of the food chain.