A method of operating an electric power system, which may include: determining a charge state of a first battery unit and a charge state of a second battery unit; determining a difference between the charge state of the first battery unit and the charge state of the second battery unit; and determining whether to enable discharging simultaneously of both the first battery unit and the second battery unit, or to enable discharging of one of the first and second battery units, based on the difference between the charge state of the first battery unit and the charge state of the second battery unit. At least one of the first and second battery units may be a swappable battery unit. The disclosure further relates to an electric power system and to a computer executable code including instructions for operating an electric power system.