What happens if my lock battery is flat and I cannot enter the home? The lock and Yale Access App will provide you with a battery warning when the battery level reaches 25% remaining battery. We strongly suggest you change the lock batteries before the batteries completely drain and the lock cannot be operated. If in the event the batteries are too low to power up the lock, the USB-C power up port can be located at the bottom of the front of the lock body. A phone can be used to power up the lock. For this you will require a USB-C to USB adapter for the phone cord to plug into. A power bank can be used to power up the lock. The power bank will require a USB-C cable to connect into the lock. When powering up the lock ensure the adapter is firmly held into the port. The covers around the adaptor can vary in size, so ensure it is in the port securely.