A method and a system for resistance seam welding of a foil and at least one foil support of a fuel cell system. During welding, the thin foil, together with the thicker foil support, is moved relative to the roller electrode while resting on a flat support element. In a suitable welding system, a counter-electrode is designed as a flat support element, such as a welding strip, that is displaceable relative to the roller electrode, the roller electrode being in rolling contact with the foil support, but not with the foil. Depending on whether one foil is to be welded to one or two foil frames, the support element may be designed having a high or a low specific electric resistance.