The present invention provides an energy storage system, particularly a battery system, that is capable of preventing self from overheating, comprising at least one energy storage unit each having two terminal posts extending outwards from the interior thereof; when there are at least two energy storage units, electrical connection therebetween is achieved by electrical connection elements that bridge the terminal posts of different energy storage units; at least one of the terminal posts and/or the electrical connection elements is in thermal connection with a heat transfer surface enlarging structure made of solid heat conductive materials. The present invention further relates to a method for preventing overheat of an energy storage system.