A portable electrical energy storage device, comprising: a first electrical energy storage cell module including a plurality of electrical energy storage cells, wherein the electrical energy storage cells in the first electrical energy storage cell module extend with their longitudinal extension along a first direction and are placed adjacent to each other in a plane which is perpendicular to the first direction, wherein each of the electrical energy storage cells in the first electrical energy storage cell module comprises, along the first direction, a first and a second longitudinal end disposed spaced apart from each other, wherein the first and the second longitudinal ends of the electrical energy storage cells in the first electrical energy storage cell module are provided with an electrical terminal, respectively; a second electrical energy storage cell module including a plurality of electrical energy storage cells, wherein the electrical energy storage cells in the second electrical energy storage cell module extend with their longitudinal extension along the first direction and are placed adjacent to each other in the plane which is perpendicular to the first direction, wherein each of the electrical energy storage cells in the second electrical energy storage cell module comprises, along the first direction, a first and a second longitudinal end disposed spaced apart from each other, wherein the first and the second longitudinal ends of the electrical energy storage cells in the second electrical energy storage cell module are provided with an electrical terminal, respectively, and wherein the second electrical energy storage cell module is positioned adjacent to the first electrical energy storage cell module along the first direction; and a first electrical energy storage cell barrier comprising a layer of a thermal insulating material and two layers of an elastic material (42, 44), wherein the layer of the thermal insulating material of the first electrical energy storage cell barrier is sandwiched between the two layers of the elastic material of the first electrical energy storage cell barrier, the first electrical energy storage cell barrier being located between the first electrical energy storage cell module and the second electrical energy storage cell module, wherein the first electrical storage cell barrier is sandwiched between the electrical terminals provided on the second longitudinal ends of the electrical energy storage cells in the first electrical energy storage cell module and the electrical terminals provided on the first longitudinal ends of the electrical energy storage cells in the second electrical energy storage cell module. a first electrical energy storage cell module including a plurality of electrical energy storage cells, wherein the electrical energy storage cells in the first electrical energy storage cell module extend with their longitudinal extension along a first direction and are placed adjacent to each other in a plane which is perpendicular to the first direction, wherein each of the electrical energy storage cells in the first electrical energy storage cell module comprises, along the first direction, a first and a second longitudinal end disposed spaced apart from each other, wherein the first and the second longitudinal ends of the electrical energy storage cells in the first electrical energy storage cell module are provided with an electrical terminal, respectively; a second electrical energy storage cell module including a plurality of electrical energy storage cells, wherein the electrical energy storage cells in the second electrical energy storage cell module extend with their longitudinal extension along the first direction and are placed adjacent to each other in the plane which is perpendicular to the first direction, wherein each of the electrical energy storage cells in the second electrical energy storage cell module comprises, along the first direction, a first and a second longitudinal end disposed spaced apart from each other, wherein the first and the second longitudinal ends of the electrical energy storage cells in the second electrical energy storage cell module are provided with an electrical terminal, respectively, and wherein the second electrical energy storage cell module is positioned adjacent to the first electrical energy storage cell module along the first direction; and a first electrical energy storage cell barrier comprising a layer of a thermal insulating material and two layers of an elastic material (42, 44), wherein the layer of the thermal insulating material of the first electrical energy storage cell barrier is sandwiched between the two layers of the elastic material of the first electrical energy storage cell barrier, the first electrical energy storage cell barrier being located between the first electrical energy storage cell module and the second electrical energy storage cell module, wherein the first electrical storage cell barrier is sandwiched between the electrical terminals provided on the second longitudinal ends of the electrical energy storage cells in the first electrical energy storage cell module and the electrical terminals provided on the first longitudinal ends of the electrical energy storage cells in the second electrical energy storage cell module.