A method for determining an operational parameter indicative of the power capability of an energy storage system of a vehicle, wherein the method comprises the steps of: - determining a state temperature of the ESS; - determining a first acceptable temperature increase of the ESS for a given time period from the determined state temperature of the ESS to a maximum temperature threshold of the ESS being defined by a safety temperature level (T max safety) of the ESS, and further determining a second acceptable temperature increase of the ESS for the given time period from the determined state temperature of the ESS to a maximum temperature threshold being defined by an operational life time temperature level (T max degrading) of the ESS, wherein the operational life time temperature level is based on the charge and discharge activity of the battery, and wherein the operational life time temperature level is lower than the safety temperature level; - determining a first maximum operational power level of the ESS for the given time period based on the determined first acceptable temperature increase of the ESS and further determining a second maximum operational power level of the ESS for the given time period based on the determined second acceptable temperature increase of the ESS; selecting the determined first maximum operational power level of the ESS if the maximum temperature threshold is the ESS safety temperature level or selecting the determined second maximum operational power level of the ESS if the maximum temperature threshold is the ESS operational life time temperature level; and controlling a temperature of the ESS based on the selected maximum operational power level of the ESS. - determining a state temperature of the ESS; - determining a first acceptable temperature increase of the ESS for a given time period from the determined state temperature of the ESS to a maximum temperature threshold of the ESS being defined by a safety temperature level (T max safety) of the ESS, and further determining a second acceptable temperature increase of the ESS for the given time period from the determined state temperature of the ESS to a maximum temperature threshold being defined by an operational life time temperature level (T max degrading) of the ESS, wherein the operational life time temperature level is based on the charge and discharge activity of the battery, and wherein the operational life time temperature level is lower than the safety temperature level; - determining a first maximum operational power level of the ESS for the given time period based on the determined first acceptable temperature increase of the ESS and further determining a second maximum operational power level of the ESS for the given time period based on the determined second acceptable temperature increase of the ESS; selecting the determined first maximum operational power level of the ESS if the maximum temperature threshold is the ESS safety temperature level or selecting the determined second maximum operational power level of the ESS if the maximum temperature threshold is the ESS operational life time temperature level; and controlling a temperature of the ESS based on the selected maximum operational power level of the ESS.