The EMPIR project LiBforSecUse aimed to develop empirical measurement models to estimate the residual capacity of second-use Li-ion battery cells with impedance-based measurement and evaluation methods. The models have been established based on a series of life cycle tests of commercial 18650 (graphite/NMC) cells including regular impedance spectroscopy and capacity measurements. The measured data are made publicly available here. They can be downloaded to verify the models established within the project and they may be used for further investigations. However, the user is asked to pay tribute to the project and the researchers providing the data by citing this data source. A pdf file is added to give more detailed information on the data.