The phases present in the positive nickel oxyhydroxide electrode (NOE) under standard operation conditions, that is, beta-Ni(OH)(2) and beta-NiOOH, were studied by powder diffraction using the Rietveld method extended to handle a range of microstructural models and high-resolution transmission electron microscopy under mild conditions. The results highlight that, contrary to what was believed, a change in the oxygen layers stacking sequence along the c-axis in beta-NiOOH (ABCA) compared to beta-Ni(OH)(2) (ABAB) takes place, which indicates that battery positive electrode material undergoes reversible structural transformations during the nickel battery charge and discharge processes.