An electrochemical energy storage device provides problem-free pressure compensation at a permanently high impermeability, includes a storage housing (1), which encases a volume, in which cells are accommodated, wherein the storage housing (1) protects the volume from the surroundings, and includes a volume compensation device (2), which compensates pressure differences between the interior of the storage housing (1) and the surroundings without a material replacement between the surroundings and the interior of the storage housing (1).