A new strategy for increasing the power density of an air-breathing small proton exchange membrane fuel cell (PEMFC) system for the main energy source of portable consumer electronics is presented. The small PEMFC system is composed of a single cell. Utilizing the output voltage of the single cell, we introduce a newly designed ultra-low voltage input boost converter. The boost converter can generate 4.1V output from input sources with low voltage ranges, such as under 1.0V. The cathode plate is made from a thin SUS 316L stainless steel plate and has ribs that prevent the cathode from bending. The hydrogen is supplied by a metal hydride (MH) tank cartridge. The MH tank contains highly packed AB5-type MH. The MH tank cartridge has a volume of 13.2cm3 and can absorb 6.7L of hydrogen. The maximum power of the small PEMFC is 4.42W at room temperature. Using 6.7L of hydrogen, the small PEMFC can generate 11Wh of electricity. The power density of the small PEMFC reaches 0.51Whcm−3. And the power density of the whole small PEMFC system, which contains the boost converter, a small Li-ion battery for a load absorber, and a case for the system, reaches 0.14Whcm−3. This value matches that of external Li-ion battery chargers for cell phones. We installed the small PEMFC system in a cell phone and confirmed the operations of calling, receiving, videophone, connecting to the Internet, and watching digital TV. And also confirmed that the small PEMFC system provides approximately 8.25h of talk time, which is about three times as long as that for the original Li-ion battery.