Batch example should explain that a file must be included when necessary

It's the comments for the batch_set($batch_definition) function

/**
 * @defgroup batch Batch operations
 * @{
 * Functions allowing forms processing to be spread out over several page
 * requests, thus ensuring that the processing does not get interrupted
 * because of a PHP timeout, while allowing the user to receive feedback
 * on the progress of the ongoing operations.
 *
 * The API is primarily designed to integrate nicely with the Form API
 * workflow, but can also be used by non-FAPI scripts (like update.php)
 * or even simple page callbacks (which should probably be used sparingly).
 *
 * Example:
 * @code
 * $batch = array(
 *   'title' => t('Exporting'),
 *   'file' => drupal_get_path('module', 'my_module') .'/my_module.batch.inc',
 *   'operations' => array(
 *     array('my_function_1', array($account->uid, 'story')),
 *     array('my_function_2', array()),
 *   ),
 *   'finished' => 'my_finished_callback',
 * );
 * batch_set($batch);
 * // only needed if not inside a form _submit handler :
 * batch_process();
 * @endcode
 *
 * Sample batch operations:
 * @code
 * // Simple and artificial: load a node of a given type for a given user
 * function my_function_1($uid, $type, &$context) {
 *   // The $context array gathers batch context information about the execution (read),
 *   // as well as 'return values' for the current operation (write)
 *   // The following keys are provided :
 *   // 'results' (read / write): The array of results gathered so far by
 *   //   the batch processing, for the current operation to append its own.
 *   // 'message' (write): A text message displayed in the progress page.
 *   // The following keys allow for multi-step operations :
 *   // 'sandbox' (read / write): An array that can be freely used to
 *   //   store persistent data between iterations. It is recommended to
 *   //   use this instead of $_SESSION, which is unsafe if the user
 *   //   continues browsing in a separate window while the batch is processing.
 *   // 'finished' (write): A float number between 0 and 1 informing
 *   //   the processing engine of the completion level for the operation.
 *   //   1 (or no value explicitly set) means the operation is finished
 *   //   and the batch processing can continue to the next operation.
 *
 *   $node = node_load(array('uid' => $uid, 'type' => $type));
 *   $context['results'][] = $node->nid .' : '. $node->title;
 *   $context['message'] = $node->title;
 * }
 *
 * // More advanced example: multi-step operation - load all nodes, five by five
 * function my_function_2(&$context) {
 *   if (empty($context['sandbox'])) {
 *     $context['sandbox']['progress'] = 0;
 *     $context['sandbox']['current_node'] = 0;
 *     $context['sandbox']['max'] = db_result(db_query('SELECT COUNT(DISTINCT nid) FROM {node}'));
 *   }
 *   $limit = 5;
 *   $result = db_query_range("SELECT nid FROM {node} WHERE nid > %d ORDER BY nid ASC", $context['sandbox']['current_node'], 0, $limit);
 *   while ($row = db_fetch_array($result)) {
 *     $node = node_load($row['nid'], NULL, TRUE);
 *     $context['results'][] = $node->nid .' : '. $node->title;
 *     $context['sandbox']['progress']++;
 *     $context['sandbox']['current_node'] = $node->nid;
 *     $context['message'] = $node->title;
 *   }
 *   if ($context['sandbox']['progress'] != $context['sandbox']['max']) {
 *     $context['finished'] = $context['sandbox']['progress'] / $context['sandbox']['max'];
 *   }
 * }
 * @endcode
 *
 * Sample 'finished' callback:
 * @code
 * function batch_test_finished($success, $results, $operations) {
 *   if ($success) {
 *     $message = format_plural(count($results), 'One post processed.', '@count posts processed.');
 *   }
 *   else {
 *     $message = t('Finished with an error.');
 *   }
 *   drupal_set_message($message);
 *   // Providing data for the redirected page is done through $_SESSION.
 *   foreach ($results as $result) {
 *     $items[] = t('Loaded node %title.', array('%title' => $result));
 *   }
 *   $_SESSION['my_batch_results'] = $items;
 * }
 * @endcode
 */

/**
 * Open a new batch.
 *
 * @param $batch
 *   An array defining the batch. The following keys can be used:
 *     'operations': an array of function calls to be performed.
 *        Example:
 *        @code
 *        array(
 *          array('my_function_1', array($arg1)),
 *          array('my_function_2', array($arg2_1, $arg2_2)),
 *        )
 *        @endcode
 *     All the other values below are optional.
 *     batch_init() provides default values for the messages.
 *     'title': title for the progress page.
 *       Defaults to t('Processing').
 *     'init_message': message displayed while the processing is initialized.
 *       Defaults to t('Initializing.').
 *     'progress_message': message displayed while processing the batch.
 *       Available placeholders are @current, @remaining, @total and @percent.
 *       Defaults to t('Remaining @remaining of @total.').
 *     'error_message': message displayed if an error occurred while processing
 *       the batch.
 *       Defaults to t('An error has occurred.').
 *     'finished': the name of a function to be executed after the batch has
 *       completed. This should be used to perform any result massaging that
 *       may be needed, and possibly save data in $_SESSION for display after
 *       final page redirection.
 *     'file': the path to the file containing the definitions of the
 *       'operations' and 'finished' functions, for instance if they don't
 *       reside in the original '.module' file. The path should be relative to
 *       the base_path(), and thus should be built using drupal_get_path().
 *
 * Operations are added as new batch sets. Batch sets are used to ensure
 * clean code independence, ensuring that several batches submitted by
 * different parts of the code (core / contrib modules) can be processed
 * correctly while not interfering or having to cope with each other. Each
 * batch set gets to specify his own UI messages, operates on its own set
 * of operations and results, and triggers its own 'finished' callback.
 * Batch sets are processed sequentially, with the progress bar starting
 * fresh for every new set.
 */
function batch_set($batch_definition) {

yeah the example (http://api.drupal.org/api/group/batch/6) is what I had problems with, after walking through the example, I got no feedback in the form of error messages from the website that my batch was not run, and given that it is a batch job it was difficult to debug and pin point the error back to the missing 'file' declaration

BTW, I thought Drupal 7 has some sort of auto loading of files feature so this may not be required any more after 6.

Awesome! Thanks for getting this committed.