Can I rebuild a cordless drill batt-pack with regular AA Ni-mh batteries?
I always do that, but I use cells of same capacity of the original cells, and the new cells must be specifically built to be welded toghether. 

A cordless drill needs much current to works, so batteries MUST be welded and not simply connected with contacts and springs. 

Also, NiMH cells will have shorter life than NiCd.