Lead-acid batteries have different uses ever since they were invented. It is found interesting and usable to investigate the ageing of battery over time, and therefore to determine the batteries cycle life and performance in different situations, remarking the automotive industry and power supply systems, among others. Nowadays lead-acid batteries with an infinite cycle life would be ideal for the applications where they are used. It is considered impossible to build an infinite cycle life battery, reason by which engineers have been looking forward to increase batteries' cycle life. The main objective of the thesis is to analyse the effect of cycle depth for the measurements data provided by the ISEA Department and to obtain each battery's rate of ageing. The finite life of the batteries is due to the occurrence of unwanted chemical or physical changes, or the loss of the active materials from which they are made; otherwise they would last indefinitely. These changes are usually irreversible and they affect the electrical performance of the cell, increasing the internal resistance, decreasing the capacity, and reducing the battery cycle life.