Batch endpoint always hits www.googleapis.com irrespective of the host setting on the StorageOptions that built the storage client.
https://github.com/GoogleCloudPlatform/google-cloud-java/blob/52b727aef88ae76984aa3c02b4d7067e198d34b7/google-cloud-storage/src/main/java/com/google/cloud/storage/spi/v1/HttpStorageRpc.java#L191