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Recent advances in energy density of Li-ion cells together with high-current fast charging ask for improved strategies for onboard safety and reliability observation of the cells. Potential degradation effects are stimulated by lithium plating and dendrite growth. The latter may ultimately cause an internal short circuit of the cell and can lead to serious damage. Increased self-discharge is an early indicator for safety-critical cell conditions. In this work, accelerated methods for self-discharge determination of Li-ion cells are presented. They are based on the analysis of cell voltage gradients during idle periods and can be applied in state-of-the-art battery management systems (BMS) performing low-drift measurement. However, transition into the idle state after driving requires a settling time of several hours before the voltage gradient can be extracted.