Why is it that NiCd batteries can be recharged?

Question

I don't need any link to a web page or something, I need to know why, and please state a scientific answer.

Answer 1

All batteries work on chemical reaction.  The chemical components of a NiCad battery were specifically designed to be able to have the chemical reaction reversed when an electric current is sent through the battery in the reverse direction.  When the chemical reaction has been completely reversed the battery is fully charged and ready to create more electric current.  

The chemicals in a standard battery weren't designed to have their reactions reversed when a current is passed through them in the reverse direction and thus the battery can't be recharged.