As a continuation of Part I, dedicated to the ground state of He‐like and Li‐like isoelectronic sequences for nuclear charges , and Part II, dedicated to two excited states of He‐like sequence, two ultra‐compact wave functions in the form of generalized Guevara–Harris–Turbiner functions are constructed for Li‐like sequence. They describe accurately the domain of applicability of the non‐relativistic Quantum Mechanics of Coulomb Charges (QMCC) for energies (2–3 significant digits [s.d.]) of the spin‐quartet state of Li‐like ions (in static approximation with point‐like, infinitely heavy nuclei). Variational parameters are fitted in by 2nd degree polynomials. The most accurate ultra‐compact function leads to the absolute accuracy a.u. for energy, and for the normalized electron‐nuclear cusp parameter for . Critical charge , where the ultra‐compact trial function for the state loses its square‐integrability, is estimated, . As a complement to Part I, square integrability for the compact functions constructed for the ground, spin‐doublet state of the Li‐like sequence is discussed. The critical charge, for which these functions stop to be normalizable, is estimated as . It implies that at —the negative helium ion He−—both states, and , exist as states embedded in the continuum.