You can merge batches whose end types are not extracts if:
They are in the same stage, and;
Their unit of measure (listed under the Quantity column) is the same, and;
They have the same production end type.
You can merge batches whose end types are extracts if their production end types are:
A combination of terpene, biomass, and sift, or;
A combination of hash types, or;
The exact same production end type.
See the main batch article for details on merging batches.