API

http://drupal.org/node/180528

EXAMPLES

http://api.drupal.org/api/group/batch_definitions

TUTORIALS

http://kevinhankens.com/content/using-drupals-batch-api
http://www.drupaler.co.uk/blog/importing-nodes-using-batch-api/480
http://mlsamuelson.com/content/getting-started-drupals-batch-api
http://www.drupalinsider.com/content/creating-batch-api-operation-parse-large-csv-file
http://thedrupalblog.com/creating-batch-api-operation-parse-large-csv-file