System for fixing a plurality of battery packs stacked one on top of the other on board a vessel, the vessel comprising a battery room whose length extends along an axis X and is delimited by a back wall, the width of which extends along a Y axis and is delimited by two lateral walls (16, 17) and the height of which extends along a Z axis and is delimited by a floor and a ceiling; each battery pack having a substantially parallelepipedal shape defining two lateral walls (22-1, 22-2), a proximal wall, a distal wall, an upper wall, and a bottom wall, each lateral wall (22-1, 22-2) defining a plurality of fixing grooves; the battery packs being intended to be disposed in several layers on the floor of the battery room between its lateral walls (16, 17) and against the back wall, the battery packs of the same layer being designed to be disposed next to each other adjacent to their lateral walls (22-1, 22-2) so that the grooves of these lateral walls (22 -1, 22-2) are arranged opposite and so that the distal walls of these packs are adjacent to the back wall; the fixing system comprises: - a plurality of lateral blocking parts, each lateral blocking part being designed to be inserted into a groove of a battery pack; the fixing system being characterized in that it further comprises: - a plurality of pitons, each piton defining a threaded lower part, a tapped upper part and an intermediate part comprising a bevelled washer; each piton being designed to be inserted into a hole formed between two opposite grooves provided with lateral blocking parts of two battery packs disposed one next to the other in a same layer and to block between the lateral walls (16, 17) the battery packs along the Y axis by interaction of the bevelled washer with the lateral blocking parts; when inserted into the corresponding hole, each piton being further designed to fix along the Z axis each layer of the upper battery packs to a lower layer of battery packs by interaction of its threaded lower part with the tapped upper part of the piton corresponding to it inserted into the hole formed between two battery packs of the lower battery pack layer. each battery pack having a substantially parallelepipedal shape defining two lateral walls (22-1, 22-2), a proximal wall, a distal wall, an upper wall, and a bottom wall, each lateral wall (22-1, 22-2) defining a plurality of fixing grooves; the battery packs being intended to be disposed in several layers on the floor of the battery room between its lateral walls (16, 17) and against the back wall, the battery packs of the same layer being designed to be disposed next to each other adjacent to their lateral walls (22-1, 22-2) so that the grooves of these lateral walls (22 -1, 22-2) are arranged opposite and so that the distal walls of these packs are adjacent to the back wall; the fixing system comprises: - a plurality of lateral blocking parts, each lateral blocking part being designed to be inserted into a groove of a battery pack; - a plurality of lateral blocking parts, each lateral blocking part being designed to be inserted into a groove of a battery pack; the fixing system being characterized in that it further comprises: - a plurality of pitons, each piton defining a threaded lower part, a tapped upper part and an intermediate part comprising a bevelled washer; - a plurality of pitons, each piton defining a threaded lower part, a tapped upper part and an intermediate part comprising a bevelled washer; each piton being designed to be inserted into a hole formed between two opposite grooves provided with lateral blocking parts of two battery packs disposed one next to the other in a same layer and to block between the lateral walls (16, 17) the battery packs along the Y axis by interaction of the bevelled washer with the lateral blocking parts; when inserted into the corresponding hole, each piton being further designed to fix along the Z axis each layer of the upper battery packs to a lower layer of battery packs by interaction of its threaded lower part with the tapped upper part of the piton corresponding to it inserted into the hole formed between two battery packs of the lower battery pack layer.