A system for wirelessly transmitting power between a mobile device and a locking device, the system comprising: a locking device comprising: a wireless power coil configured to receive power; an authentication module configured to receive and authenticate an access credential, the authentication module operatively connected to a lock actuator, the lock actuator configured to lock or unlock a mechanical or electronic lock when the access credential is authenticated; and at least one battery configured to supply power to at least the lock actuator, the at least one battery comprising a storage of power, the at least one battery configured to store at least a portion of power received by the wireless power coil; a mobile device comprising: a wireless power coil configured to wirelessly transmit power to the wireless power coil of the locking device; a communication module configured to transmit the access credential to the authentication module of the locking device; and at least one battery configured to supply power to at least the wireless power coil, at least a portion of the power transferred from the mobile device to the locking device being from the at least one battery; wherein the power is wirelessly transmitted from the mobile device to the locking device when the storage of power is below a critical level, characterised in that the authentication module of the locking device is configured to transmit a confirmation signal to the communication module of the mobile device when the access credential is authenticated, the confirmation signal comprising instructions to charge the at least one battery of the locking device, when the storage of power is below the critical level, and the wireless power coil of the mobile device is configured to wirelessly transmit power to the wireless power coil of the locking device if the confirmation signal is not received within a threshold time. a locking device comprising: a wireless power coil configured to receive power; an authentication module configured to receive and authenticate an access credential, the authentication module operatively connected to a lock actuator, the lock actuator configured to lock or unlock a mechanical or electronic lock when the access credential is authenticated; and at least one battery configured to supply power to at least the lock actuator, the at least one battery comprising a storage of power, the at least one battery configured to store at least a portion of power received by the wireless power coil; a wireless power coil configured to receive power; an authentication module configured to receive and authenticate an access credential, the authentication module operatively connected to a lock actuator, the lock actuator configured to lock or unlock a mechanical or electronic lock when the access credential is authenticated; and at least one battery configured to supply power to at least the lock actuator, the at least one battery comprising a storage of power, the at least one battery configured to store at least a portion of power received by the wireless power coil; a mobile device comprising: a wireless power coil configured to wirelessly transmit power to the wireless power coil of the locking device; a communication module configured to transmit the access credential to the authentication module of the locking device; and at least one battery configured to supply power to at least the wireless power coil, at least a portion of the power transferred from the mobile device to the locking device being from the at least one battery; a wireless power coil configured to wirelessly transmit power to the wireless power coil of the locking device; a communication module configured to transmit the access credential to the authentication module of the locking device; and at least one battery configured to supply power to at least the wireless power coil, at least a portion of the power transferred from the mobile device to the locking device being from the at least one battery; wherein the power is wirelessly transmitted from the mobile device to the locking device when the storage of power is below a critical level, characterised in that the authentication module of the locking device is configured to transmit a confirmation signal to the communication module of the mobile device when the access credential is authenticated, the confirmation signal comprising instructions to charge the at least one battery of the locking device, when the storage of power is below the critical level, and the wireless power coil of the mobile device is configured to wirelessly transmit power to the wireless power coil of the locking device if the confirmation signal is not received within a threshold time.