Recharge one's batteries (4)
I believe the answer is:
rest
'recharge one's batteries' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for rest that I've seen before include "Remainder; be inactive" , "Support for putting things on" , "'Relax, pause from work (4)'" , "Repose - remainder" , "Relax, take a break" .)