You can also check the list at the bottom of this page as some battery suppliers will also delivery and replace it on site for you
http://www.nbnco.com.au/connect-home-or-business/already-connected/nbn-equipment/battery-back-up-service-information.html
http://www.nbnco.com.au/connect-home-or-business/already-connected/nbn-equipment/battery-back-up-service-information.html