We show that the considered in previous paper [1] lepton bag model, generating the external gravitational and electromagnetic fields of the Kerr-Newman (KN) solution is supersymmetric and represents a BPSsaturated soliton, interpolating between internal vacuum state and external KN solution. We obtain Bogomolnyi equations for this phase transition, and show that Bogomolnyi bound determines all important features of this bag model, including its stable shape. In particular, for stationary KN solution the BPS-bound provides stability of the ellipsoidal form of the bag and formation of the ring-string structure at its border, while for the periodic electromagnetic excitations of the KN solution, the BPS-bound controls deformation of the surface of the bag, reproducing the known flexibility of bag models. This paper is extension of the work [1], in which we considered the gravitating lepton bag model based on the Kerr-Newman (KN) black hole solution.It has been discussed long ago that black holes may be connected with elementary particles. However, the spin/mass ratio of elementary particles is extreme large, and the corresponding black hole loses the horizons, turning into an ultra-extreme (over-charged and over-rotating) KN solution with a naked singular ring, which forms a topological defect of space-time. As usual, emergence of singularity is a hint for generalization of the theory, and the Kerr singular ring created the problem of source of the KN solution. This problem proved to be very complicated, and this year we can mark the 50th anniversary of its discussions. Earlier attempts to build a source of the KN solution where discussed by Israel in [2], and Israel referred to the paper by Newman and Janis 1965 [3], wherein nontriviality of this problem was at first indicated. Carter obtained in [4] that the KN solution has gyromagnetic ratio g = 2, corresponding to that of the Dirac electron, and starting from this fact, Israel suggested in [2] a classical model of the electron based on a rotating disklike source of the KN solution, enclosed by the Kerr singular ring.The consistent regular model of the KN source was suggested by López, who built the KN source as a rotating vacuum bubble, covering the Kerr singular ring. In the same time, many properties of the KN source indicated its close relationships with string models [5,6,7,8], and resolution of this duality was coming from the disklike soliton model [9], in which the vacuum internal state of the López bubble-source was replaced by a superconducting false-vacuum formed by the Higgs mechanism of symmetry breaking. The ring-string emerged in this model as a narrow tube of the electromagnetic (EM) potential concentrated at the sharp border of the disklike source, similar to the well-known Nielsen-Olesen vortex string model in the Landau-Ginzburg theory [10].Recently, this model was generalized to a gravitating bag model [1], for which one of the known features is a flexibility and ability to create stringlike structures 1Principal peculiarity of the model consi...