The small fuel cell is being researched as an alternative power source to the Li-ion battery in mobile phone. In this paper, a direct hydrogen fuel cell system which powers a mobile phone without a supplementary battery is compactly integrated below 25 ml volume at the backside of the phone. The system consists of a small (8 ml) metal hydride hydrogen storage tank with 4 L hydrogen storage or an energy density of similar to 640 W h/L, a thin air-breathing planar polymer electrolyte membrane fuel cell (PEMFC) stack (13.44 cm(2) x 3 mm for a volumetric power density of 335 W/L), miniature pressure regulator, and a high efficiency DC-DC voltage converting circuitry. The hydrogen storage tank is packed with the AB(5) type metal hydride alloy. The eight-cell air-breathing planar stack (8 ml) is very thin (3 mm) due to a thin flexible printed circuit board current collectors as well as a unique riveting assembly and is capable of a robust performance of 2.68 W (200 mW/cm(2)). A miniature pressure regulator is compact with fluidic and electrical connections within 4 ml. A miniature DC-DC voltage converter operates at an overall efficiency of 90%. Consequently, the estimated energy density of a fully integrated fuel cell system is 205 W h/L (70.5 W h/kg). (C) 2014 Elsevier Ltd. All rights reserved.