In order send bulk reminders on batch level, you can:
1. Click on "Courses" in the side navigation bar.
2. Select "Batches" from the drop-down.
3. Click on the batch for which reminders are to be sent.
4. Click on the "Settings" tab on the top-right corner of your screen.
5. Select "Invitations" from the drop-down as shown in the screenshot below.
6. Set the "Status" filter to "Not Registered" or "Registered Not Enrolled"
7. Filter from here to show the number of entries.
8. Check the box against course to send reminders in bulk. You can also select the users whom you want to send the reminders.
9. Once you have selected the users to whom you intend to send reminders, Click on "Send Reminder".