Due to the energy revolution, the need for sustainable energy sources is higher than ever. For the process of decoupling the energy production from the energy consumption, thermal energy storage systems with high capacities are being used. In this paper, experimental investigations on the transient behavior on a packed-bed thermal energy storage were conducted. The pilot plant uses the principle of sensible heat storage. In this case, the energy charge and discharge is induced through an alteration of the temperature of the storage mass. Air is primarily being used as the heat transfer medium for the supply and the removal of energy. The air is warmed up by a heating coil with a maximum power of 15 kWth. Gravel with an average grain diameter of 6 mm and a filling weight of 595 kg is being used as the storage material. The evaluation of the first measurements provided physically unrealistic data due to flap leak. After sealing the flaps, the air mass flow can only stream in one direction (from the bottom to the top) through the container with the storage mass during the phase of loading and unloading. In the usable temperature range of 50265C, the regenerator can store 45,78 kWh of energy with a maximum power of 9.98 kW during a cycle. The energy density in the useful temperature range is 82160 kWh per m. The highest efficiency of 89.09 % of all the test series was achieved at a mass flow of 250 kg/h. In summary it can be said that an increase of the mass flow has a positive effect on the cycle times and the degree of the utilization rate. At a mass flow of 150 kg/h and with about 1000 Pa, gravel has a more than 12-times differential pressure compared to the previous measurements on the ballast bed (30mm). When taking a closer look at the measured values of previous test series with the ballast bed and the now gained knowledge about the leaky blocking flaps, the measurement results are falsified and therefore the comparison of the gravel with the ballast bed is not suitable. The goal of this paper was achieved by being now able to compare successfully the examined parameters such as the storable energy, power and energy density and other essential parameters with other similar test facilities.