Batch numbers differ from serial numbers in a very simple way. Serial numbers are assigned for single unit products, like mobile phones or custom made dresses. These are items that you need to track by the unit. For example, you’d want to know exactly which mobile phone the customer has bought in order to make an exchange.
Batch numbers are used for groups of products that only need to be differentiated from the next batch of that same product. For example, you don’t need to know exactly which individual box of cookies your customer bought, but if there is an issue with it you will benefit from knowing the batch it belonged to.
Note that the same product can not have both a batch number and a serial number.