For UPS applications such as the mobile phone base station, the selection of PEM fuel cell technology seems only feasible for the case of a heavy-duty service time requirement. The weight reduction of the whole energy system using fuel cell technology is significant, and the volume and the cost can also be superior when the service time is over 24 h. If the production cost and the module volume of fuel cell system can be further reduced, the results will be more promising. (C) 2004 Published by Elsevier B.V.