Stopper for closing and sealing an opening in a housing of an energy storage system and energy storage system

A stopper for closing and sealing an opening in a housing of an energy storage system, wherein the stopper comprises the following:

• a connecting region which is configured to come into engagement with the opening of the energy storage system;
• and
• a sealing region which is arranged above the connecting region in an axial direction of the stopper,
• wherein the sealing region is configured to receive a sealing element which is designed to be deformed by a force completely acting in the axial direction of the stopper when the stopper is in an installed state, such that a sealing effect of the sealing element is created by the force completely acting in the axial direction of the stopper, wherein a cross-section of the sealing element has an L shape both when the stopper is in the installed and when the stopper is in an uninstalled state, wherein the sealing element comprises a first portion on a side of the sealing element facing the connecting region and a second portion on a side of the sealing element facing away from the connecting region, wherein the second portion of the sealing element comprises an outer diameter in a radial direction of the stopper that is, both in the installed and the uninstalled state of the stopper, greater than the outer diameter in the radial direction of the stopper of the first portion, and wherein the sealing element is formed so as to be completely circumferential and rotationally symmetrical.