  We present improved estimates of the electric charge that black holes could
hold when these are embedded in the ionised plasma within galaxies. We have
implemented the spontaneous emission of charges of opposite sign to that of the
black hole via athermal Hawking evaporation, including its dependence on black
hole spin, and we have estimated the equilibrium charge that arises as this
charge loss is balanced by the continuous accretion of charges from the
surrounding plasma. The resulting charge can be several orders of magnitude
lower than previously estimated upper limits, but it can surpass the pair
production limit noted by Gibbons (1974) by a margin that increases with the
amplitude of the black hole spin and the density of the plasma. We also
implement a calculation for the net charge of galaxies due to their stellar
black holes and to primordial black holes in the case these make up a fraction
of the dark matter. We find that these charges lie within the range that would
produce adequate magnetic field seeds at the onset of galaxy formation.
