You are confusing perl. According to perldoc -f grep, you have two choices:

grep BLOCK LIST
grep EXPR,LIST
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Your usage is a hybrid of the two, as the curly braces indicate the beginning of a block. Both of these two forms work

scalar( grep m[\d{3}-\d{3}], values %batch_ids ) == 6;
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or

scalar( grep { m[\d{3}-\d{3}] } values %batch_ids ) == 6;
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mikfire