The present work aims to contributing to the perspective of using lead acid batteries for the storage of energy produced by photovoltaic plants. After a review of different models tackling the performance of lead acid batteries, we opted for the electrochemical approach and based our study on the evolution of the electrolyte specific gravity during charge/discharge cycling tests of a 12 V lead acid battery. The test results revealed a drop of the specific gravity of the electrolyte during successive C/D cycling. This is reflected by the maxima (1.2463 g/cm3–1.1697 g/cm3) and the minima (1.1273 g/cm3–1.106 g/cm3) of the specific gravity values after uninterrupted tests, revealing underlying irreversible reactions. Further data collection and analysis will serve as building blocks for an operational model.