A low temperature energy storage unit able to store 36 J between 11 K and 20 K is described. Thanks to an enthalpy reservoir connected to the cold finger of a cryocooler by a heat switch, this device allows measurements in a completely vibration-free environment during a long time after the cryocooler stop. The ESU described in this article uses lead as enthalpy reservoir (9 cm(3)) and a H-2 gas gap heat switch. Tests varying the initial temperature and the input power were performed. A test showed that a platform can be stabilized at 19 K during more than 1 h using this ESU. The temperature drifts measured after stopping the cryocooler are compared to simulations. A very good agreement is obtained allowing scaling up devices if longer periods are required. (C) 2009 Elsevier Ltd. All rights reserved.