One of my battle backgrounds broke, pls help

Looks like either corrupted tiles or a corrupted tilemap. Check this page for a list of offsets containing the battle background tile data.
http://www.angelfire.com/pq/jumparound/f...fsets.html

I believe the tilemaps' locations are documented in the ROM map on the FF6hacking Wiki. Not which is which, but where they all are, at least. You could just reinsert the entire range of data from a clean ROM and see if that fixes things.