  The quasinormal resonance spectrum $\{\omega_n(\mu,q,M,Q)\}_{n=0}^{n=\infty}$
of charged massive scalar fields in the charged Reissner-Nordstr\"om black-hole
spacetime is studied {\it analytically} in the large-coupling regime $qQ\gg
M\mu$ (here $\{\mu, q\}$ are respectively the mass and charge coupling constant
of the field, and $\{M,Q\}$ are respectively the mass and electric charge of
the black hole). This physical system provides a striking illustration for the
validity of the universal relaxation bound $\tau \times T \geq \hbar/\pi$ in
black-hole physics (here $\tau\equiv 1/\Im\omega_0$ is the characteristic
relaxation time of the composed black-hole-scalar-field system, and $T$ is the
Bekenstein-Hawking temperature of the black hole). In particular, it is shown
that the relaxation dynamics of charged massive scalar fields in the charged
Reissner-Nordstr\"om black-hole spacetime may {\it saturate} this quantum
time-times-temperature inequality. Interestingly, we prove that potential
violations of the bound by light scalar fields are excluded by the
Schwinger-type pair-production mechanism (a vacuum polarization effect), a {\it
quantum} phenomenon which restricts the physical parameters of the composed
black-hole-charged-field system to the regime $qQ\ll M^2\mu^2/\hbar$.
