Heated battles approaching sea (6)
I believe the answer is:
warmed
'heated' is the definition.
(thesaurus)
'battles approaching sea' is the wordplay.
'battles' becomes 'war' (I've seen this in other clues).
'approaching' means one lot of letters go next to another.
'sea' becomes 'med' (abbreviation of Mediterranean**).
'war'+'med'='WARMED'
(Other definitions for warmed that I've seen before include "Heated" , "gave enthusiasm" , "given thermal treatment" .)