Lithium-ion batteries continue to transform consumer electronics, mobility, and energy storage sectors, and the applications and demands for batteries keep growing. Supply limitations and costs may lead to counterfeit cells in the supply chain that could affect quality, safety, and reliability of batteries. Our research included studies of counterfeit and low-quality lithium-ion cells, and our observations on the differences between these and original ones, as well as the significant safety implications, are discussed. The counterfeit cells did not include internal protective devices such as the positive temperature coefficient or current interrupt devices that typically offer protection against external short circuits and overcharge conditions, respectively, in cells from original manufacturers. Poor-quality materials and lack of engineering knowledge were also evident on analyses of the electrodes and separators from low-quality manufacturers. When the low-quality cells were subjected to off-nominal conditions, they experienced high temperature, electrolyte leakage, thermal runaway, and fire. In contrast, the authentic lithium-ion cells performed as expected. Recommendations are provided to identify and avoid counterfeit and low-quality lithium-ion cells and batteries.