Electrochemical device for storing electrical energy in rectangular geometric cells, narrow stack geometry, comprising: a straight sturdy rectangular parallelepiped-shaped housing made of a material resistant to oxidizing conditions with good mechanical strength, and which is hermetically sealed, an electrode stack with rectangular narrow stack geometry housed inside the housing , comprising a stack of positive electrodes inserted on one metal rod following the sequence: a positive electrode a positive electrode separating element a stack of negative electrodes inserted on another metal rod following the sequence a negative electrode a negative electrode-separating element characterized in that said housing comprises a base provided with a metal substrate fitted with through holes , a cover , a front side (4.1), a rear side (4.2), wherein each of said front and rear sides (4.1, 4.2) is provided with an inner chamber , the metal rods are hollow rods that serve as current collectors and as means for cooling, which run over the metal substrate of the base and through its through holes , and wherein the electrochemical device further comprises: two metal plates fitted with central holes , wherein each metal plate is incorporated in each inner chamber of each side (4.1, 4.2), two metal-ion sheets , two grids , each one screwed to each of the metal plates holding one of the metal-ion sheets between them, and metal external connections that connect with the metal-ion sheets through the central holes of the metal plates . a straight sturdy rectangular parallelepiped-shaped housing made of a material resistant to oxidizing conditions with good mechanical strength, and which is hermetically sealed, an electrode stack with rectangular narrow stack geometry housed inside the housing , comprising a stack of positive electrodes inserted on one metal rod following the sequence: a positive electrode a positive electrode separating element a stack of negative electrodes inserted on another metal rod following the sequence a negative electrode a negative electrode-separating element a stack of positive electrodes inserted on one metal rod following the sequence: a positive electrode a positive electrode separating element a positive electrode a positive electrode separating element a stack of negative electrodes inserted on another metal rod following the sequence a negative electrode a negative electrode-separating element a negative electrode a negative electrode-separating element said housing comprises a base provided with a metal substrate fitted with through holes , a cover , a front side (4.1), a rear side (4.2), wherein each of said front and rear sides (4.1, 4.2) is provided with an inner chamber , the metal rods are hollow rods that serve as current collectors and as means for cooling, which run over the metal substrate of the base and through its through holes , two metal plates fitted with central holes , wherein each metal plate is incorporated in each inner chamber of each side (4.1, 4.2), two metal-ion sheets , two grids , each one screwed to each of the metal plates holding one of the metal-ion sheets between them, and metal external connections that connect with the metal-ion sheets through the central holes of the metal plates . <EOS>