Electronic and structural aspects of a MnO2 electrode in a rechargeable MnO2/Zn battery environment have been investigated by in situ Mn K-edge x-ray absorption fine structure (XAFS). The relative amplitudes of the three major Fourier transform shells of the extended. XAFS function of the rechargeable MnO2 electrode in the undischarged state were similar to those found for ramsdellite, a MnO2 polymorph with substantial corner-sharing linkages among the basic MnO6 octahedral units. The analyses of the background-subtracted pre-edge peaks and absorption edge regions for the nominally l-e(-) discharged electrode were consistent with Mn3+ as being the predominant constituent species, rather than a mixture of Mn4+ and Mn2+ sites. Furthermore, careful inspection of both the x-ray absorption near edge structure and EXAFS indicated that the full recharge of NnO(2), which had been previously discharged either by one or two equivalent electrons, generates a material with decreased corner-sharing linkages compared to the original undischarged MnO2.