A motor vehicle, particularly a passenger car, contains an onboard electrical system having a number of electrical consumers, a generator and an onboard electrical system rechargeable battery. A bidirectional interface is provided for a rechargeable device battery of a mobile device such that the rechargeable device battery can be coupled to the onboard electrical system by the bidirectional interface and, when coupled, can both be charged by the onboard electrical system and be used as an additional energy source in the onboard electrical system.