A METHOD OF CONTROLLING A VEHICLE ELECTRICAL SYSTEM

The invention relates to a method () of controlling a vehicle electrical energy storage system having a plurality of battery units connectable to form a battery unit assembly for providing traction power to a vehicle electric propulsion system. The method comprises the steps of selecting () a plurality of sub-sets of battery units from the plurality of battery units, determining () an alternative operational power (AOPn) of the electrical energy storage system for each sub-set of the plurality of selected sub-sets of battery units, and for the plurality of selected sub-sets of battery units, identify () the sub-set having the highest alternative operational power for providing power to the electric propulsion system among the plurality of sub-sets of battery units.