Hi,
I get the following exception using the batch() api on AppEngine Flex.

    batch = vision_client.batch()
    for blob in blobs:
            content = blob.download_as_string()
            image = vision_client.image(content=content)
            batch.add_image(image, FEATURES)
    results = batch.detect()

DEBUG:google_auth_httplib2:Making request: POST https://accounts.google.com/o/oauth2/token
ERROR:root:Exception occurred in retry method that was not classified as transient
<class 'google.gax.errors.RetryError'>

Package:
google-cloud-vision (0.23.2)