NOVELTY - A battery stack arrangement comprises at least one spacing element (61), e.g. folded plate or pins arranged between two mounting units. The spacing element abuts against at least one endplate of a bipolar battery and is held in place by a mounting frame to create a stack pressure, independent of a sealing pressure, which stack pressure is controlled by a tie unit.    USE - For bipolar batteries in hybrid vehicles.    ADVANTAGE - The spacing elements will provide the desired feature of separating the seal pressure from the stack pressure if they are brought in direct physical contact with at least one of the endplates of each battery through openings in the casing. They will ensure that the internal electrical connection of the stacked batteries, having two batteries connected in series, is established. The battery stack arrangement permits the internal resistance to be maintained at an acceptable level during normal operation independently of the pressure needed to create a sealed bipolar battery.    DETAILED DESCRIPTION - A battery stack arrangement comprises at least one bipolar battery (51a, 51b) having battery cell arranged between a positive endplate (22) and a negative endplate (23). Each battery cell is provided with a seal (24) arranged around the entire periphery of each cell. A sealing pressure is applied over the seal to prevent electrolyte leakage between adjacent cells. The battery stack arrangement comprises a mounting frame (57) including at least two mounting units (59) and at least one tie unit (60, 60', 60") holding the mounting units together. The bipolar battery is arranged between two mounting units. The battery stack arrangement comprises at least one spacing element arranged between the mounting units. The spacing element abuts against at least one endplate of the battery and is held in place by the mounting frame to create a stack pressure, independent of the sealing pressure, which stack pressure is controlled by the tie unit. The spacing element is made from an electrically conducting material.    DESCRIPTION OF DRAWING(S) - The figure is a battery stack arrangement.    Positive endplate (22)    Negative endplate (23)    Seal (24)    Bipolar battery (51a, 51b)    Mounting frame (57)    Mounting units (59)    Tie unit (60, 60', 60")    Spacing element (61)