Key Code Lockout will come on after the battery is reconnected if the status is different to when it was disconnected and will go out after 30 minutes. While it is displayed you will not be able to enter the EKA. You do not have to buy anything, except maybe a door latch if it has a faulty microswitch (but even then there is a way of fooling the system as long as the doors are unlocked. Whenever the battery is disconnected do it with all doors shut but unlocked (or the drivers door open but the other closed). Then reconnect in the same state and it won't even know you have had the battery off.