The Fraunhofer Institute for Solar Energy Systems ISE has developed a fuel cell system to power a portable computer. The components are a four-cell polymer electrolyte membrane fuel cell (PEMFC) system, a six-phase DC/DC-converter, an air pump, two cylindrical metal hydride storage tanks, a valve and a pressure sensor to adjust the hydrogen flow [national patent applied, DE 101 19 339, 03 (2001)] and a control unit for the management of the whole system. Prominent characteristics of the system are a flat design of the fuel cell stack and the integrated DC/DC-converter [national patent granted, DE 198 10 556 C1, 11 (1999)]. The system provides a nominal power output of about 42W at 12V. Extensive physical investigations of different flow field combinations as well as the system design are presented.