  The analogy between the restricted primitive model and capacitor circuits,
originally described decades ago for the Mean Spherical Approximation, is
explored to demonstrate its transferability in linearized electrolyte theories.
On this basis, we offer an explanation of why treating the salt diameter as a
free adjustable parameter blurs differences between electrolyte theories in the
calculation of mean ionic activity coefficients. Furthermore, a capacitor
circuit analogy with an approximation of the Dressed Ion Theory is applied to
develop a modified closest approach parameter "b" for the Pitzer-Debye-H\"uckel
term. This modification is able to account for the qualitative effects of over-
and underscreening in the calculation of mean ionic activity coefficients. This
is achieved by defining "b" as a semi-empirical function that allows close
resemblance with the multiple decay-length extension of the Debye-H\"uckel
theory for high dielectric constant values and that lies close to recommended
literature values of "b" for low dielectric constant values. Finally, as proof
of principle, this modified semi-empirical Pitzer-Debye-H\"uckel term is
implemented in the predictive COSMO-RS-ES model, an own reimplementation of the
COSMO-RS theory developed for thermodynamic property calculations of
electrolyte systems. It is shown that the modified semi-empirical
Pitzer-Debye-H\"uckel term is an effective replacement for the recently
published version of COSMO-RS-ES with explicit considerations for ion pairing.
This reduces the modelling complexity by implicitly considering ion pairing and
improves overall qualitative performance for the prediction of salt
solubilities in mixed-solvent systems and even mean ionic activity coefficients
in non-aqueous media.
