Nickel-__ (nicd) Battery; Rechargeable Power Cell
Puzzle 13 of Energy Sources Hard Pack
Question is: Nickel-__ (nicd) Battery; Rechargeable Power Cell
and the answer is: CADMIUM
Word Meaning:
CADMIUM — A chemical element (symbol Cd) with an atomic number of 48: a soft, silvery-white metal.
Definitions from Wiktionary.