Battery room in the monastery (4)
I believe the answer is:
cell
This clue might be a double definition.
'battery' is the first definition.
(I've seen this in another clue)
'room in the monastery' is the second definition.
'cell' can be an answer for 'room' (cell is a kind of room). I am not certain of the 'in the monastery' bit.
Can you help me to learn more?
(Other definitions for cell that I've seen before include "The basic structural unit of all organisms" , "Lock-up room" , "Microscopic unit of living matter" , "Monastic room" , "Small room for nun, monk or prisoner" .)