I found this lying around my hard drive. It's a Python 3 script that creates a corresponding SAV file for every NES ROM it finds with the battery backed save specified. Sharing it in case it's useful to anybody else.
Edit: Python scripts were later disallowed on this forum. Uploading a ZIP with what I think was the original script.
Edit: Python scripts were later disallowed on this forum. Uploading a ZIP with what I think was the original script.