Copper sheathes this rod used in battery? (9)

I believe the answer is:

truncheon

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'copper sheathes this rod used in battery?' is the definition.
'truncheon' can be an answer for 'rod' (thesaurus). I am unsure of the rest of the definition.

This is the entire clue.

Can you help me to learn more?

(Other definitions for truncheon that I've seen before include "Police baton" , "Policeman's traditional weapon" , "Police weapon" , "Peelers' baton" , "Police staff" .)

I've seen this clue in The Independent.

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