Exhausted, as a battery (4)
I believe the answer is:
dead
'exhausted as a battery' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for dead that I've seen before include "Lifeless" , "Pushing up the daisies" , "Insensitive" , "No longer relevant" , "Unresponsive" .)