  We exploit once again the analogy between the energy-momentum tensor and the
so-called ``superenergy'' tensors in order to build conserved currents in the
presence of Killing vectors. First of all, we derive the divergence-free
property of the gravitational superenergy currents under very general
circumstances, even if the superenergy tensor is not divergence-free itself.
The associated conserved quantities are explicitly computed for the
Reissner-Nordstrom and Schwarzschild solutions. The remaining cases, when the
above currents are not conserved, lead to the possibility of an interchange of
some superenergy quantities between the gravitational and other physical fields
in such a manner that the total, mixed, current may be conserved. Actually,
this possibility has been recently proved to hold for the Einstein-Klein-Gordon
system of field equations. By using an adequate family of known exact
solutions, we present explicit and completely non-obvious examples of such
mixed conserved currents.
