Small fuel cells are considered likely replacements for batteries in portable power applications. In this paper, the performance of a 2 cm x 2.4 cm x 1.4 cm passive miniature air breathing direct formic acid fuel cell (DFAFC) at room temperature is reported. The cell produced current density up to 250 mA/cm(2) and power density up to 33 mW/cm(2) at ambient conditions. The fuel cell runs successfully with formic acid concentration ranging from 1.8 and 10 M with little degradation in performance. These results show that passive fuel cells can compete with batteries in portable power applications. (C) 2003 Elsevier B.V. All rights reserved.