  We start from a static, spherically symmetric space-time in the presence of
an electrostatic field and construct the mini-superspace Lagrangian that
reproduces the well known Reissner - Nordstr\"om solution. We identify the
classical integrals of motion that are to be mapped to quantum observables and
which are associated with the mass and charge. Their eigenvalue equations are
used as supplementary conditions to the Wheeler-DeWitt equation and a link is
provided between the existence of an horizon and to whether the spectrum of the
observables is fully discrete or not. For each case we provide an orthonormal
basis of states as emerges through the process of canonical quantization.
