Regarded as the future of the automotive industry, electric cars are not far from a worldwide deployment. However some drawbacks still slow down this deployment such as batteries lifetime and autonomy which have to be increased in order to compete conventional internal combustion engine vehicles (ICE). Therefore, a well understanding of the battery aging phenomena is mandatory regarding the development of new hybrid achitectures and their energy management. In order to study those phenomena and understand the causes, ten fuel cell hybrid electric vehicles developed for postal delivery purpose among the european Mobypost project have been monitored during three years. This experimentation led to create a rich database. Using this database the remaining capacity of an entire fleet of vehicule have been calculated. Consequently the capacity fades could be estimated and illustrated in function of the temperature and the batteries cycle number, through a non linear regression with an error NRMSE of 0.129.