Abstract: The invention relates to an authentication and/or energy auditing system for a plug-in electric drive vehicle. A first device connects to a first power apparatus and establishes an electrical power path between the first and a remote device. The latter is connectable to a second power apparatus. The authentication system preferably includes a powerline transceiver to receive a request containing an identifier from the remote device over the power path. Control means controls operation of the first device and responds to the request to initiate an authentication process to determine whether or not the remote device is authentic and authorised to exchange power with the first device, and to activate a control switch to electrically connect the first device to the first power apparatus only upon an authentic and authorised determination.