Setting Batch for existing items , seems to be the answer.
So cannot do it midway, a possible but difficult workaround would be to:
- Duplicate the items and make the original item inactive.
- Rename the old item, so that the same name can be used for future transactions.
- Create new BOMs wherever the old item is being used
- Use BOM update tool to replace the all the Old BOMs
This is a lot of work, I will have to manage without Batch nos. for now.