The electrical resistivity and heat capacity of the silver-doped lanthanum manganites La0.80Ag0.15MnO3 and La0.85Ag0.15MnO3 have been investigated. Despite the nonstoichiometry of the composition, the La0.80Ag0.15MnO3 manganite exhibits a bulk homogeneity and better physical properties from the applied point of view as compared to the La0.85Ag0.15MnO3 manganite, viz., the former compound has a higher spontaneous magnetoresistance and a larger jump of the heat capacity with a small width of the phase transition, and the anomalies of the heat capacity and electrical resistivity in the vicinity of the Curie point of this compound agree with the fluctuation nature of the second-order phase transition. The behavior of the properties of lanthanum-deficient manganites under investigation in the region of the phase transition is consistent with the classical theory of indirect exchange interaction. The behavior of the temperature dependence of the electrical resistivity has been analyzed in terms of two models. One of these models is based on the tunneling of charge carriers between ferrons or polarons, and the other model is based on the polaron hopping conduction. Both approaches lead to consistent results, and their combination has made it possible to estimate the tunneling distance of charge carriers. The origin of the influence of technological parameters characterizing the synthesis of La1 − xAgyMnO3 ceramic materials on their physical properties has been elucidated.