$db["default"]["hostname"] = "localhost";
$db["default"]["username"] = "username";
$db["default"]["password"] = "password";
$db["default"]["database"] = "database";

$db["userdatabase"]["hostname"] = "localhost";
$db["userdatabase"]["username"] = "username";
$db["userdatabase"]["password"] = "password";
$db["userdatabase"]["database"] = "database";

$this->load->database('userdatabase');
// Do user stuff
$this->load->database('default');