This horse presumably will never run free (7)
I believe the answer is:
charger
'this horse presumably will never' is the definition.
'charger' can be an answer for 'horse' (charger is a type of horse). I'm unsure of the remainder of the definition.
'run free' is the wordplay.
'run' becomes 'charge'.
'free' becomes 'r' (I can't justify this - if you can you should give a lot more credence to this answer).
'charge'+'r'='CHARGER'
Can you help me to learn more?
(Other definitions for charger that I've seen before include "Electrical device - old warhorse" , "I expect payment" , "old dish" , "One loading" , "One asking money for" .)