Electrochemical reactions of lithium with cubic alpha-Li2ZnGe and with hexagonal Li2ZnSi have been studied. Charging a Li/alpha-Li2ZnGe battery results in lithium extraction to yield a Li1.2ZnGe composition, through a first step at ca. 0.9 V that involves a phase transition from cubic to hexagonal, and a second step at ca. 1.1 V where Ge and Zn segregation is observed. By discharge of the Li/alpha-Li2ZnGe battery, the composition Li3ZnGe is reached at 0.2 V while the cubic structure is maintained. Lithium insertion into Li2ZnSi preserves the hexagonal structure. but lithium extraction modifies the X-ray diffraction pattern.