The coding is right and works as you could see in the Display converted data step.
The usual error people make with BAPIs is that they miss to care about the corresponding fields in X-structures
In this case with the batch indicator it is even more important to know what your batch level setting is, because SAP knows 2 batch management fields, one at MARA (batch level is client or material level) and one at MARC (batch level is plant level).