1. An energy storage system case comprising:a body unit comprising a battery accommodating unit configured to accommodate a plurality of batteries, and a control module mounting unit comprising a mounting plate on both sides of which control modules are configured to be mounted to control charge/discharge of the plurality of batteries, the mounting plate having an opening extending from a first side of the mounting plate to a second side of the mounting plate opposite the first side;
a casing cover coupled to the body unit to face the first side of the mounting plate; and
a heat-dissipation unit located opposite the casing cover and coupled to the mounting plate to dissipate heat generated by a first control module among the control modules to an outside thereof,
wherein the heat-dissipation unit is coupled to the second side of the mounting plate to completely block the opening such that a space between the mounting plate and the casing cover is sealed from an external environment.