Combined soft and solid state chemistry followed by precise XRD investigations allow us to determine the Li-V-O system as well as the structural modifications induced by Li insertion in silver vanadates. On the base of these studies we propose an interpretation of both Li//V2O5 and Li//Ag2V4O11 batteries electrochemical behavior. In the I<x<3 domain, disproportionation of V4+, occurs leading to the formation of different mixtures between lithium vanadates and vanadium oxides. The different domains are related to the different steps observed in the Li//V2O5 discharge curve. It is also demonstrated that the sprouting phenomenon occurring in the Ag1+xV3O8 vanadate induces the formation of a new phase Ag2V4O11 instead of the oxygen deficient form Ag2V4O11-y. According single crystal XRD structural determination this phase is shown to be isostructural with Li1+xV3O8. Electrochemical Li insertion starts with the reduction of Ag+ leading to the lithiated phase meaning that whatever the starting phase used, the main insertion process occurs in Li1+xV3O8.