In order to fire off a script-fu script from batch mode, there are a few basic steps required. The first is modifying or writing a script to be useful in a non-interactive context.
The second step is launch the batch job with the proper arguments and commands. Easier said than done.
That being said, it should be pointed out there are some serious caveats with using gimp in batch mode. Pretty much any script designed for interactive use is going to need to be modified. Also, the batch mode parser is very very weak. It doesnt even support all the standard script-fu data types, most noticebly, colors. Scripts can be rewritten to avoid this however.