The electric performances of direct borohydride fuel cells (DBFCs) are evaluated in terms of power density and life time with respect to the NaBH4 concentration. A DBFC constituted of an anionic membrane, a 0.6 mg(pt) cm(-2) anode and a commercial non-platinum based cathode led to performances as high as 200 mW cm(-2) at room temperature and with natural convection of air. Electrochemical life time test at 0.55 mA cm(-2) with a 5 M NaBH4/1 M NaOH solution shows a voltage diminution of 1 mV h(-1) and a drastic drop of performances after 250 h. The life time is twice longer with 2 M NaBH4/1 M NaOH solution (450 h) and the voltage decrease is 0.5 mV h(-1). Analyses of the components after life time tests indicate that voltage loss is mainly due to the degradation of the cathode performance. Crystallisation of carbonate and borate is observed at the cathode side, although the anionic membrane displays low permeability to borohydride. (C) 2009 Elsevier B.V. All rights reserved.