BatchWriteItem and BatchWriter are two methods used in Amazon's DynamoDB for batch operations. BatchWriteItem is a low-level API method that enables you to put or delete several items across multiple tables in a single API call. However, the complexity lies in handling unprocessed items and exceptions. On the other hand, BatchWriter is a high-level API provided by boto3, the AWS SDK for Python, that abstracts the details of adding automatic retries and handling unprocessed items. BatchWriter simplifies batch operations, managing the complexity under the hood while offering an easier interface for writing multiple items.