A fastening system for at least one battery in a vehicle, which fastening system comprises - at least one elongated support bar with a first length and a first and a second end (121A, 121B), and presenting a first and a second side (122A, 122B), wherein the second side of the support bar is adapted so as to be arranged in abutment against a top of said battery, characterized in that the support bar has, viewed in its longitudinal direction, a U-shaped cross-section comprising two side parts and one intermediate part presenting a first and a second side (122A, 122B) and that the system further comprises; - at least one elongated sprung rail with a second length and a first and a second end (131A, 131B), and presenting a first and a second side (132A, 132B) wherein the sprung rail is adapted so as to be arranged in the U-shaped support bar, - wherein the second length is greater than the first length, - wherein the sprung rail comprises a first and a second recess (133A, 133B) arranged at respective first and second ends (131A, 131B), and wherein said first and second recesses (132A, 132B) are adapted so as to receive fastening elements, comprising a nut, a threaded rod, on which the nut is adapted so as to be arranged, and a washer, which is adapted so as to be arranged between the nut and the sprung rail and wherein the threaded rod is adapted to be disposed in connection to a vehicle chassis or a longitudinal supporting beam and - wherein the second side of the sprung rail is adapted so as to be arranged against the first side of the support bar in order to transfer a force from said sprung rail to said support bar in order to hold the battery securely. - at least one elongated support bar with a first length and a first and a second end (121A, 121B), and presenting a first and a second side (122A, 122B), wherein the second side of the support bar is adapted so as to be arranged in abutment against a top of said battery, characterized in that the support bar has, viewed in its longitudinal direction, a U-shaped cross-section comprising two side parts and one intermediate part presenting a first and a second side (122A, 122B) and that the system further comprises; - at least one elongated sprung rail with a second length and a first and a second end (131A, 131B), and presenting a first and a second side (132A, 132B) wherein the sprung rail is adapted so as to be arranged in the U-shaped support bar, - wherein the second length is greater than the first length, - wherein the sprung rail comprises a first and a second recess (133A, 133B) arranged at respective first and second ends (131A, 131B), and wherein said first and second recesses (132A, 132B) are adapted so as to receive fastening elements, comprising a nut, a threaded rod, on which the nut is adapted so as to be arranged, and a washer, which is adapted so as to be arranged between the nut and the sprung rail and wherein the threaded rod is adapted to be disposed in connection to a vehicle chassis or a longitudinal supporting beam and - wherein the second side of the sprung rail is adapted so as to be arranged against the first side of the support bar in order to transfer a force from said sprung rail to said support bar in order to hold the battery securely.