It can energise a mobile horse (7)

I believe the answer is:

charger

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'horse' is the definition.
(charger is a type of horse)

I can't explain the remainder of the clue.

(Other definitions for charger that I've seen before include "One may provide juice" , "One asking money for" , "One demanding payment" , "Horse; flat dish" , "A warhorse; a serving-dish" .)

I've seen this clue in The Guardian.

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