Methods and apparatuses for determining a battery capacity are described. According to one embodiment, an exemplary method includes generating virtual calibration data of the battery based on one or more characteristics of the battery, determining a virtual open circuit voltage (Voc) of the battery while the battery is being used, and estimating the capacity of the battery based on the determined virtual open circuit voltage of the battery and the virtual calibration data of the battery, while the battery is being used.