The Battery Lock is a Lock in Granny and is located at the Main Door. The lock is added in Hard Mode or if the player chooses the Extra Locks option. The Battery is required to open this lock.
The lock is seemingly made out of metal with a vertical wooden bar and a small handle. The handle turns to the left when the Battery isn't placed in and turns to the right when the Battery is placed in.
The Player has to put the Battery in there. When done so; the handle will turn right and the wooden bar will slowly push itself with each other and then the lock is unlocked. It will also make a noise which alerts Granny.
When you use the Battery on the lock, it will make a low-pitched sound similar to a wind-up toy (presumably made by the lock). This sound will alert Granny.
It is the only lock which is used to unlock with a electric "key" which is the Battery.
It is the only lock which makes the longest noise.