Different accelerated tests in 12 fuel cells stack were performed in laboratory, namely on/off, back-up, and base-load regimes. In parallel, membrane electrode assemblies (MEA) were integrated in two "on-site" systems for GSM relay application. One of them was dedicated to base-load power applications while the second fuel cells coupled with photovoltaic panels operated in semibase load mode. To investigate the influence of the power profiles on MEA degradation, over 80 CCB MEAs (5 layers) were studied at different scales using ex situ characterizations such as tensile tests, TGA-MS, DMTA, and SEM. A series of complementary microstructural ageing markers were thereby identified. The isolated influence of dry-wet cycling on MEA properties was also established after passive hydro-thermal (HT) ageing performed continuously for 10 months in the laboratory. The changes of each marker as a function of HT ageing time permitted to define a temporal benchmark. Based on these indicators, the main changes occurred in the MEA properties appear after a 5 months dry-humid cycling (up to about 1800 cycles). The trends observed were useful to compare and estimate the degree of degradation of each ageing tests. Thus, the accelerated tests performed in laboratory for at least 500 h in stack did not reveal systematic MEA modifications. On the contrary, the 1500 h "on-site" system operation results in some MEA degradations which origins are discussed. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 120: 3501-3510, 2011