Drupal - Drush Scripting? Or Batch API?

I would not suggest to use the batch API, simply for the fact that batch operations depend from the browser; if for any reason the browser crashes, or it loses the connection with the server, the batch operations will not terminate, or (worse) they will be hanging. In fact, to avoid PHP timeouts, the batch operations cause the browser to ping the batch page at intervals; that is what happens, whenever JavaScript code is involved, or not (in the later case, Drupal uses the refresh meta tag).

In these cases, Drush is probably a better choice; you can create a custom module that implements specific Drush commands, or simply add a command file in the directory Drush uses for its commands.

Also you may use custom PHP CLI script. Here is a simple example for drupal 7:

#!/usr/bin/php
<?php
echo "Ubercart tasks\n===================\n";

$_SERVER['HTTP_HOST']       = 'default';
$_SERVER['PHP_SELF']        = '/index.php';
$_SERVER['REMOTE_ADDR']     = '127.0.0.1';
$_SERVER['SERVER_SOFTWARE'] = NULL;
$_SERVER['REQUEST_METHOD']  = 'GET';
$_SERVER['QUERY_STRING']    = '';
$_SERVER['PHP_SELF']        = $_SERVER['REQUEST_URI'] = '/';
$_SERVER['HTTP_USER_AGENT'] = 'console';

define('DRUPAL_ROOT', getcwd());
require_once DRUPAL_ROOT . '/includes/bootstrap.inc';
drupal_bootstrap(DRUPAL_BOOTSTRAP_FULL);
//-------------------------------------------

// Place your code here