If anyone else facing issue with using structured outputs for batch api, i have found this works the easiest.
Define your schema using Pydantic , then you can convert it to OAI compliant strict json schema using to_strict_json_schema function available in the python client. (though a private method and ugly, this was much easier and more reliable than other 3rd party libraries that have not been tested extensively).
from openai.lib._pydantic import to_strict_json_schema