The number of records to send to the function in each batch. For a standard queue, this can be up to 10,000 records. For a FIFO queue, the maximum is 10. For a batch size over 10, you must also set the batch window (MaximumBatchingWindowInSeconds) to at least 1 second.

https://docs.aws.amazon.com/lambda/latest/dg/with-sqs.html