As electrochemical power sources technologies, namely Li-ion batteries and PEM fuel cells, continue advancing, ways to extend their lifespan have to be pursued. With prognostics and health management (PHM) approach, several techniques can provide estimation of state of health (SOH) and prediction of remaining useful life (RUL) in order to help the manufacturers improving performance. Before developing a solution, PHM issues need to be properly defined, in particular in terms of deterioration/ageing indicators used for SOH estimation and RUL prediction. This paper reviews the ageing phenomena of batteries and fuel cells in order to investigate how to define suitable degradation indicators for these devices. Since Li-ion battery' PHM is much more developed, their similarities and differences have thus been studied as an exploration path of how proton exchange membrane fuel cell (PEMFC) could benefit from the battery knowledge and experience feedback. Even if no innovative solutions are emerging, the relevance of the covariates used for PEMFC and batteries ageing indicators are argued, providing a first step to build a suitable PHM approach for electrochemical devices.