We show that the γ(III)/β(II) phase transition is at the origin of the second plateau at 0.8V in the Ni-based batteries by means of transmission electron microscopy (TEM) and X-ray diffraction (XRD) studies and intermittent galvanostatic measurements (GITT). This study shows that the equilibrium voltage of this transition is 1.25V vs Cd-Cd(OH)2, thus implying an overvoltage of 400 mV. Direct evidence for a textural memory effect trough the γ(III)/β(II) phase transition is given by TEM studies. The reoxidation of the β(II) phase to γ(III) phase occurs without going trough the β(III) phase.