Small Power Source for Toys, Remotes
Puzzle 1 of Aquarium Easy Pack
Question is: Small Power Source for Toys, Remotes
and the answer is: BATTERY
Word Meaning:
BATTERY — (electricity, electronics, countable) A device used to power electric devices, consisting of one or more electrically connected electrochemical cells or (archaically) electrostatic cells.
Definitions from Wiktionary.