This is another business ruleJust realized that I should have said that each "Batch of Donations" must have a unique Batch Date

This time your approach is OK. You have ONE BatchDate TO MANY donations relationship.
Note please that you always should use a NUMBER (preferable an AUTO NUMBER) as PK, even if the data in a field has no duplicates (I refer to your BatchDate table where, if I remember well, you have the field BatchDate - of type Date/Time - as the primary key).