Flat __; Car Power Source That Needs Recharging
Puzzle 15 of Flat Things Easy Pack
Question is: Flat __; Car Power Source That Needs Recharging
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.