What actually helps with homework battles?

Reduce the number of decisions and the emotional load. A consistent time and place removes the daily negotiation about when. Sit nearby without hovering, so help is available but the work is theirs. Break it into visible chunks with short breaks, since the perceived size is usually what triggers resistance. Resist correcting everything, because homework the teacher believes is the child's work is more useful than a perfect submission. If it routinely takes far longer than the school expects, that is worth raising with the teacher rather than absorbing at home every evening.