Abstract.Batteries have been used in a lot of different applications for a quite large time period, in particular in solar photovoltaic energy. In spite of this fact, their ageing mechanisms turn out to be still deeply out of control. We show in this paper the results of applying the evolution of a preliminary method for the estimation of lead-acid batteries state of health which is based on the Root Mean Square Error (RMSE) between voltage distributions throughout a time period of nine years. A complete set of batteries, concerning the main parameters that could influence their lifetime, was analised.