Some electronic locks have a terminal on the outside for a 9V battery in case the internal batteries die. For example: http://www.interlock.com.sg/index.php/pr

Some electronic locks have a terminal on the outside for a 9V battery in case the internal batteries die. For example: http://www.interlock.com.sg/index.php/products/gateman-digital-locks/gateman-a20-fd-a20fhh http://www.interlock.com.sg/index.php/products/gateman-digit... No mechanical key and no emergency battery terminal? Better have another door.