Method of preparation of lithium battery

A method for preparing lithium-ion and lithium-ion polymer batteries to reduce water content and cell impedance. A battery having improved calendar life is prepared by electrochemically treating the activated cell by applying a voltage to the cell to react oxygen provided or trapped in the cell with moisture present as an unavoidable impurity. The electrochemical treatment of the present invention decreases the water content in the cell, thereby lowering cell impedance and extending battery life.