A series of gamma-MnO2 with Mn4+ cation vacancy fraction 1.5 < x < 2.3 was prepared via chemical synthesis. X-ray diffraction (XRD) revealed high degree of microtwinning (T-w > 70%) and de Wolff disorder ( 0.32 < P-r < 0.35) in the prepared samples. Thermal analysis showed four-stage decomposition corresponding to the removal of physical water, chemisorbed water, formation of Mn2O3 and Mn3O4, respectively. The chemical composition and physical properties of the prepared samples were expressed in terms of Ruetschi's cation vacancy model for MnO2. The discharge behavior in 9 M KOH was governed by homogeneous solid-state reduction wherein protons and electrons were simultaneously inserted into MnO2 lattice. Their electrochemical behavior was also studied by performing cyclic voltammetry in 9 M KOH. An attempt was made to correlate obtained energy density as a function of proton transfer rate during the discharge process.