Arsenal half-heartedly topped up (5)
I believe the answer is:
depot
'arsenal' is the definition.
(thesaurus)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for depot that I've seen before include "Terminus for transport vehicles" , "storeroom" , "Depository for goods" , "Military HQ" , "Headquarters - storehouse" .)