Bandage what's been damaged before the end of the battle (6)
I believe the answer is:
swathe
'bandage' is the definition.
(I know that swathe is a type of bandage)
'what's been damaged before the end of the battle' is the wordplay.
'been damaged' indicates an anagram.
'before' is a charade indicator (letters next to each other).
'the end of the' says to take the final letters.
The final letter of 'battle' is 'e'.
'whats' is an anagram of 'swath'.
'swath'+'e'='SWATHE'
(Other definitions for swathe that I've seen before include "considerable cut" , "Broad strip or area of something" , "Wrap in layers of, say, bandages" , "Wrap; a cut strip" , "Wrap in layers of warm garments or bandages" .)