Google Calendar API batch request PHP

<?php
require_once(APPPATH . 'libraries/Google/Client.php');
require_once(APPPATH . 'libraries/Google/Http/Batch.php');
require_once(APPPATH . 'libraries/Google/Service/Calendar.php');

class My_google_calendar
{
  ...

  /** Add single Event for Student */
  function addEvent($lesson, $instructor, $return_request = false, $enable_attendees = false)
  {
    $calendar = $this->getGoogleCalendar(); // get calendar service variable

    $lesson_from = date(DATE_RFC3339, $lesson->from);
    $lesson_to = date(DATE_RFC3339, $lesson->from + $lesson->duration); 

    $event = new Google_Service_Calendar_Event();
    $event->setSummary('Lesson with student: '$lesson->student_full_name);

    $start = new Google_Service_Calendar_EventDateTime();
    $start->setDateTime($lesson_from); 
    $start->setTimeZone($this->getGoogleCalendarTimeZone());
    $event->setStart($start);

    $end = new Google_Service_Calendar_EventDateTime();
    $end->setDateTime($lesson_to);
    $end->setTimeZone($this->getGoogleCalendarTimeZone());
    $event->setEnd($end);
    $event->setColorId(4);

    $description = "...";
    $event->setDescription($description);

    if (isset($student->email) && $enable_attendees) {
      $attendee1 = new Google_Service_Calendar_EventAttendee();
      $attendee1->setResponseStatus('needsAction');
      $attendee1->setEmail($student->email);
      $attendees = array($attendee1);
      $event->setAttendees($attendees);
    }

    $createdEvent = $this->calendar->events->insert($this->calendar_id, $event, array('fields' => 'id'));
    return $return_request ? $createdEvent : $createdEvent->getId();
  }

  /** Push group of events to the Calendar */
  function multipleInsert ($lessons, $instructor)
  {
    $this->use_batch = true;
    $this->client->setUseBatch($this->use_batch);
    $batch = new Google_Http_Batch($this->client);
    $optParams = array('fields' => 'status,updates');

    foreach($lessons as $time => $lesson) {      
        $lesson = array_shift($group['lessons']);
        $req = $this->addEvent($lesson, $instructor, true);
        $batch->add($req, $time);
      }
    }
    $results = $batch->execute();

    return $results;
  }

}

$batch = $service->createBatch();

$batch = new Google_Http_Batch($this->client);