When the batteries are very low, a warning will be given. When the warning is heard, the batteries should be replaced as soon as possible.
If the batteries have completely died, there is a back-up power connection port on the underside of the outer lock, to which a 9V battery can be connected to provide power to the lock to open the lock in this event.
It is important to replace the batteries as soon as the lower power warning is heard or if you have had to use a power bank to open the lock.
