Offence committed in cell (7)
I believe the answer is:
battery
This clue could be a double definition.
'offence' is the first definition.
(I have seen 'violent offence' mean 'battery' so perhaps 'offence' could also mean 'battery')
'committed in cell' is the second definition.
'battery' can be an answer for 'cell' (thesaurus). I am not sure about the 'committed in' bit.
Can you help me to learn more?
(Other definitions for battery that I've seen before include "Group of cells (or guns)" , "Means of storing electric current" , "One's charged" , "Source of charge" , "criminal offence" .)