A battery cell comprising: a frame formed from a non-electrically conductive material, the frame having a frame thickness (Tf); a cell core surrounded by and entirely within the frame and having a cell-core thickness (Tc), the cell core comprising at least one anode, at least one cathode and at least one electrolyte between the at least one anode and the at least one cathode; and, wherein the cell-core thickness (Tc) is less than or equal to the frame thickness (Tf) during cell-charge and/or cell-discharge cycling, and the battery cell further comprising: a conductive anode-current collector extending over a portion of the non-electrically conductive material forming the frame, the conductive anode-current collector in electrical contact with the at least one anode; and a conductive cathode-current collector extending over and in electrical contact with a portion of the at least one cathode, the conductive cathode-current collector exposed through and accessible at a surface of the non-electrically conductive material forming the frame characterized in that the battery cell is a solid state battery cell, comprising: at least one cell-core swell-accommodating recess surrounded by and entirely within the frame, the at least one cell-core swell-accommodating recess defining an internal cell volume into which the cell core is expandable and from which the cell core is contractible, and wherein the frame is mounted on the at least one cathode. a frame formed from a non-electrically conductive material, the frame having a frame thickness (Tf); a cell core surrounded by and entirely within the frame and having a cell-core thickness (Tc), the cell core comprising at least one anode, at least one cathode and at least one electrolyte between the at least one anode and the at least one cathode; and, wherein the cell-core thickness (Tc) is less than or equal to the frame thickness (Tf) during cell-charge and/or cell-discharge cycling, and the battery cell further comprising: a conductive anode-current collector extending over a portion of the non-electrically conductive material forming the frame, the conductive anode-current collector in electrical contact with the at least one anode; and a conductive cathode-current collector extending over and in electrical contact with a portion of the at least one cathode, the conductive cathode-current collector exposed through and accessible at a surface of the non-electrically conductive material forming the frame characterized in that the battery cell is a solid state battery cell, comprising: at least one cell-core swell-accommodating recess surrounded by and entirely within the frame, the at least one cell-core swell-accommodating recess defining an internal cell volume into which the cell core is expandable and from which the cell core is contractible, and wherein the frame is mounted on the at least one cathode. a conductive anode-current collector extending over a portion of the non-electrically conductive material forming the frame, the conductive anode-current collector in electrical contact with the at least one anode; and a conductive cathode-current collector extending over and in electrical contact with a portion of the at least one cathode, the conductive cathode-current collector exposed through and accessible at a surface of the non-electrically conductive material forming the frame characterized in that the battery cell is a solid state battery cell, comprising: at least one cell-core swell-accommodating recess surrounded by and entirely within the frame, the at least one cell-core swell-accommodating recess defining an internal cell volume into which the cell core is expandable and from which the cell core is contractible, and wherein the frame is mounted on the at least one cathode.