A method for mounting a battery system to a chassis floor of an electrical vehicle is provided, wherein the battery system is adapted for providing electrical power for driving rolling movement of said electrical vehicle, and wherein a plane extends through and parallel to said chassis floor with a first side of said plane facing in a downward direction during use of the electrical vehicle, the method including: fixing a plurality of battery modules to the chassis floor at the first side of said plane, each battery module including electrical terminals; subsequently electrically connecting the electrical terminals of the battery modules to each other to form the battery system; and fixing a cover plate to the chassis floor such that the cover plate covers the battery modules. A vehicle chassis and a vehicle including such a chassis are provided as well.