This is a high energy storage unit for supplying power to a sound module (LGB 65000-65004) or to existing sound locomotives in analog operation when the power pack is shut off. This lets you hear the sounds for a time after a locomotive comes to a stop. On MTS layouts, the track is always powered, and this accessory is not necessary. See also 65000, 65001, 65002, 65003, 65004, and 17050.