The electrostatic interactions between two spherical particles, each bearing a charged surface layer, are investigated. Based on the assumption that the thickness of this layer is relatively greater than the Debye length, approximate values for the potential distribution and the electrostatic interaction energy are derived. The present study extends a recent analysis in which two charged porous spherical particles are considered. We show that the latter can be recovered as a limiting case of the former. We found that the difference in the permittivity of the bulk solution and that of the membrane has a significant effect on both the potential distribution and the electrostatic interaction energy; the assumption that these permittivities are the same, as in most of the relevant studies, may lead to a significant deviation. Also, the use of an averaged value of a nonuniform fixed-charge distribution to simulate its effect on the interactions between two particles may lead to a significant deviation, and therefore, knowing the exact fixed-charge distribution becomes essential in practice.