  We develop a double mean-field theory for charged macrogels immersed in
electrolyte solutions in the spirit of the cell model approach. We first
demonstrate that the equilibrium sampling of a single explicit coarse-grained
charged polymer in a cell yields accurate predictions of the swelling
equilibrium if the geometry is suitably chosen and all pressure contributions
have been incorporated accurately. We then replace the explicit flexible chain
by a suitably modeled penetrable charged rod that allows to compute all
pressure terms within the Poisson-Boltzmann approximation. This model, albeit
computationally cheap, yields excellent predictions of swelling equilibria
under varying chain length, polymer charge fraction, and external reservoir
salt concentrations when compared to coarse-grained molecular dynamics
simulations of charged macrogels. We present an extension of the model to the
experimentally relevant cases of pH-sensitive gels.
