The batch checkouts feature introduced by bug 11759, adds a BatchCheckoutsValidCategories syspref which is a free-text one. It is expected to be filled with pipe-separated patron categories. The syspref should be removed, and this should be moved to the categories table: - A checkbox on editing patron categories (conditional to the BatchCheckouts syspref value) - A new column: categories.allow_batch_checkouts
The system preference has since be changed and is now a nice multi-select presenting the different available patron categories. I think it's nice that you can set up the feature with a lot less clicks this way than it would be if this was moved to the patron category and we have nice UX now. Closing, please reopen if you disagree!