Definition from Wiktionary, the free dictionary
fight a losing battle
- To continue to wage war when it is clear that one is not going to win.
- (idiomatic)To try to do something so difficult that it will probably end in failure.
- 1984, Lucy Gore, Diary Of A Working Mum, p18
- The bus was oppressively warm and the air-conditioning was fighting a losing battle with the heat.