Batteries in prison? (5)

I believe the answer is:

cells

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'batteries in prison?' is the definition.
The definition and answer can be both man-made objects as well as being plural nouns.
Perhaps they are linked in a way I don't understand?

This is the entire clue.

Can you help me to learn more?

(Other definitions for cells that I've seen before include "Mobile phone in the US" , "Rooms for prisoners" , "Basic structural units of all organisms" , "Accommodation for prisoners" , "Small rooms" .)

I've seen this clue in the Sydney Morning Herald.

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