This paper aims to study the undesirable aging process or malfunctions state of the lead acid batteries using the fault and causal tree analysis during lead acid battery operation and during manufacturing process. The causal tree analysis presents the various possible combinations of events that involve the stratification of the electrolyte, the sulfating of the electrodes and the adherence loss of active mass to the grid. The parameters of electrical model are identified in order to found the degree of battery's degradation. The experimental determination of the variation interval of the parameters is done according to each of degradation mode. These modes are used in a diagnosis system allowing the identification of the depth of each aging process of the lead acid battery.