It heavily depended on the chemical of the battery. In the Lifepo4 Battery Pack used in ITS's series PHEV, the charging characteristic showed that it could charge faster at around 40% of SOC, similar to what Tseng [19] found in its journal. At around 30% to 50%, the LiFePO4 battery is around its maximum charging efficiency, and the amount of current drawn is in balance with the change of the voltage, thus higher energy drawn. ...... constant voltage charging circuit is designed for a 12V 10Ah LiFePO4 battery pack to keep the charging voltage constant and allow the charging current to be less than 3C which let charging current between in conventional charging and fast charging areas. The charging data is shown in Table 2. When the time is 0 for start, the initial value of the voltage is 11.48V, and the charging current is 30A. ...