An autonomous cardiac implant, in particular of the leadless capsule type, comprising: - a tubular body; - surface electrodes (70, 72) carried by the tubular body; - an energy harvesting module adapted to convert external stresses applied to the implant into electrical energy, comprising an inertial pendular unit including an elastically deformable element coupled to an inertial mass; - a rechargeable battery adapted to be charged by the energy harvesting module, the battery being previously charged to an initial charge level; and - an interface circuit adapted to selectively couple the surface electrodes (70, 72) to the rechargeable battery, said implant being characterized in that the interface circuit comprises a switching circuit (88-94; 88-100) adapted to operate a switching between: • a transport and storage configuration in which, before implantation of the implant, the surface electrodes (70, 72) are connected (66, 68) to a link (78, 80) coupling to an external source forming an electrical energy reserve, the external source being physically separated from the implant, the interface circuit being adapted, in said transport and storage configuration, to receive a power supply from the external source and to provide said power supply to the rechargeable battery, and • a functional configuration, in which the surface electrodes (70, 72) are decoupled from the external source after the implant has been implanted, in that at least one of the surface electrodes is an auxiliary electrode that is not an electrode for pacing/detecting cardiac potentials, and in that: • in the transport and storage configuration, the interface circuit is adapted to couple the auxiliary electrode to the rechargeable battery of the implant, and • in the functional configuration, the interface circuit is adapted to decouple the auxiliary electrode from the rechargeable battery of the implant, and is adapted to put the auxiliary electrode to a floating potential. - a tubular body; - surface electrodes (70, 72) carried by the tubular body; - an energy harvesting module adapted to convert external stresses applied to the implant into electrical energy, comprising an inertial pendular unit including an elastically deformable element coupled to an inertial mass; - a rechargeable battery adapted to be charged by the energy harvesting module, the battery being previously charged to an initial charge level; and - an interface circuit adapted to selectively couple the surface electrodes (70, 72) to the rechargeable battery, • a transport and storage configuration in which, before implantation of the implant, the surface electrodes (70, 72) are connected (66, 68) to a link (78, 80) coupling to an external source forming an electrical energy reserve, the external source being physically separated from the implant, the interface circuit being adapted, in said transport and storage configuration, to receive a power supply from the external source and to provide said power supply to the rechargeable battery, and • a functional configuration, in which the surface electrodes (70, 72) are decoupled from the external source after the implant has been implanted, • in the transport and storage configuration, the interface circuit is adapted to couple the auxiliary electrode to the rechargeable battery of the implant, and • in the functional configuration, the interface circuit is adapted to decouple the auxiliary electrode from the rechargeable battery of the implant, and is adapted to put the auxiliary electrode to a floating potential.