Electrical energy system with fuel cells

A method of operating an energy system for a vehicle, the energy system including a fuel cell, a high-voltage battery, a direct-current converter with electrical isolation arranged between the fuel cell and the high-voltage battery, and a mains charging device connected between the fuel cell and the direct-current converter, wherein the mains charging device contains a rectifier but no DC-to-DC converter with electrical isolation, the method comprising:

• electrically connecting the fuel cell to the direct-current converter;
• electrically connecting the high-voltage battery to the direct-current converter;
• adapting fuel cell power, by the direct-current converter, and passing adapted fuel cell power to the high-voltage battery;
• charging the high-voltage battery by using the rectifier to rectify a mains voltage and passing the rectified mains voltage on to the high-voltage battery via the direct-current converter arranged between the fuel cell and the high-voltage battery;
• and
• electrically isolating, by the direct-current converter, the high-voltage battery from the mains voltage.