A maturation process for an electric battery cell comprises charging the electric battery cell, subjecting the electric battery cell to a maturation period of at least one day while no electrical load other than a measurement apparatus is connected to the electric battery cell, and taking at least one measurement of the open circuit voltage of the electric battery cell during the maturation period using the measurement apparatus. The measurement apparatus is incorporated into a structure of the electric battery cell, forming an integral part of the electric battery cell. The maturation process further comprises determining whether electric battery cell is defective in dependence on the at least one measurement.