A method for monitoring battery ageing of a battery unit in an energy storage system of a vehicle or a vessel, the method comprising: - predicting an expected service life of the battery unit based on at least information relating to a planned usage of the battery unit, wherein predicting the expected service life of the battery unit comprises: ∘ creating (S1-1) a set of battery usage classifications, wherein each battery usage classification is associated with at least one set of predefined operating parameter ranges, ∘ for each battery usage classification, determining (S1-2) at least one expected ageing curve (1, 2, 3) associated with each battery usage classification, ∘ classifying (S1-3) the planned usage of the battery unit in accordance with the set of battery usage classifications, wherein the prediction of the expected service life is determined based on the at least one expected ageing curve of the battery usage classification associated with the classified planned usage, - during usage of the battery unit, obtaining operational data relating to an actual usage of the battery unit, - predicting an actual service life of the battery unit based on at least the obtained operational data, wherein predicting the actual service life of the battery unit comprises classifying the actual usage of the battery unit in accordance with the set of battery usage classifications, the predicted actual service life of the battery unit being determined based on the at least one expected ageing curve (1, 2, 3) of the battery usage classification associated with the classified actual usage, - comparing the predicted actual service life with the predicted expected service life, thus obtaining a comparison result; - determining whether a predetermined notification criterion is fulfilled based on the comparison result, - generating a notification to a user of the battery unit if the predetermined notification criterion is fulfilled. - predicting an expected service life of the battery unit based on at least information relating to a planned usage of the battery unit, wherein predicting the expected service life of the battery unit comprises: ∘ creating (S1-1) a set of battery usage classifications, wherein each battery usage classification is associated with at least one set of predefined operating parameter ranges, ∘ for each battery usage classification, determining (S1-2) at least one expected ageing curve (1, 2, 3) associated with each battery usage classification, ∘ classifying (S1-3) the planned usage of the battery unit in accordance with the set of battery usage classifications, wherein the prediction of the expected service life is determined based on the at least one expected ageing curve of the battery usage classification associated with the classified planned usage, ∘ creating (S1-1) a set of battery usage classifications, wherein each battery usage classification is associated with at least one set of predefined operating parameter ranges, ∘ for each battery usage classification, determining (S1-2) at least one expected ageing curve (1, 2, 3) associated with each battery usage classification, ∘ classifying (S1-3) the planned usage of the battery unit in accordance with the set of battery usage classifications, - during usage of the battery unit, obtaining operational data relating to an actual usage of the battery unit, - predicting an actual service life of the battery unit based on at least the obtained operational data, wherein predicting the actual service life of the battery unit comprises classifying the actual usage of the battery unit in accordance with the set of battery usage classifications, the predicted actual service life of the battery unit being determined based on the at least one expected ageing curve (1, 2, 3) of the battery usage classification associated with the classified actual usage, - comparing the predicted actual service life with the predicted expected service life, thus obtaining a comparison result; - determining whether a predetermined notification criterion is fulfilled based on the comparison result, - generating a notification to a user of the battery unit if the predetermined notification criterion is fulfilled.