MnV2O6+delta. nH(2)O (0 < delta < 1) amorphous oxides were prepared by a two-step process including the precipitation of a crystallized precursor MnV2O6 . 4H(2)O and its ozonation at temperatures below 100 degrees C. Their characterization by spectroscopic techniques (XAS and EELS) shows that V5+ retains a VO5 environment and that Mn, which remains in octahedral coordination, is oxidized to Mn4+ mainly. MnV2O6+delta compounds insert reversibly large amounts of Li per formula unit ( e.g. Li(12)MnV2O(6.96)) at low voltage. After the first insertion/de-insertion cycle, subsequent cycles correspond to fully reversible lithium insertion between the two compositions: LialphaMnV2O6+delta (alpha greater than or equal to 2) and Li(12)MnV(2)Ob(6+delta) (from 600 to 900 mAh/g). Investigations on the Li derivatives by XAS and EELS show that during the insertion/de-insertion cycles the V oxidation state varies reversibly between +5 and +3, Mn4+ cations are reduced to Mn2+ upon the first discharge. During the subsequent cycles the average Mn oxidation state varies reversibly between +2 and about +2.6. It clearly appears that the electron transfer from Li to the host matrix decreases with increasing x in Li(x)MuV(2)O(6+delta).