In this paper the notion of capacitance (F) of a capacitor, equivalent to incremental capacity analysis and to differential capacity analysis, is linked to the notion of a reservoir form of an electrochemical element. Experiments applied to different electrochemical systems such as supercapacitor, Zn/MnO₂ battery, NiMH cell and Li-Ion cell show that the reservoir curve seems to be a good signature of these systems. The reservoir curve allows the characterisation of the charge storage facility, the aging and thermal effects in electrochemical batteries.