This paper presents a methodology used to assess the State of Health (SOH) of lithium-ion batteries. This methodology can be readily embedded in all battery management devices including the electronics for electric vehicles. The smart estimation method is based on a Fuzzy Logic System (FLS) and two calculated battery's parameters. Therefore it enhances the SOH value based primarily on both the calendar and the cycling life. The FLS is constructed by using only the temperature and the absolute value of the current that the battery sustains. Finally, through the experiments, obtained results for both a new and an aged battery demonstrate the accuracy of the methodology and how it can improve the battery's lifespan