this paper analyzes the ageing experienced by six different types of batteries used into a large scale grid-connected PV plant that participates in the electricity market and, therefore, has to generate the energy in a controlled way in order to cope with the hourly-production bids matched in the market and minimize deviations since these imply economic penalties. Due to the inherent variability of the PV production, the batteries will assure this controllability goal. The work presented performs a systematic analysis throughout one whole year of operation and uses the rain flow counting algorithm in order to determine the number of cycles experienced by the batteries. Finally, using the cycling capacity curves provided by the battery manufacturers', the total ageing suffered in one year of operation as well as the life expectancies of the batteries are calculated. All the analyses conducted in this paper are based on actual data recorded from an operative PV power plant and use verified models.