“…Several SOC models have been proposed in the literature (e.g., Piller, et al, 2001, Pop, et al, 2005, which can be grouped in the following categories: i) measurement of electrolyte specific gravity, ii) battery current time-integration, iii) battery impedance/resistance estimation, iv) measurement of the battery open circuit voltage, v) models that take into account the electrolyte temperature, discharge rate and other batteries parameters. Additionally, an accurate SOC estimation needs to take into account the battery environmental conditions, with particular reference to its temperature, as well as the battery behaviour at different discharge rates.…”