A method controls electrical connection of a plurality of battery packs of an electric energy storage system of a vehicle to a load during operation of the vehicle. The plurality of battery packs are configured to be selectively connected in parallel to the load. Based on at least an operational mode of the electric energy storage system and on the voltage of each one of the battery packs, and by allowing simultaneous connection of at least two battery packs to the load, proposing a connection sequence for electrically connecting at least a subset of the plurality of battery packs to the load. Prior to connecting at least the subset of battery packs to the load, and based on at least an internal resistance of each one of the battery packs within at least the subset of battery packs, determining whether the proposed connection sequence fulfils a predetermined connection condition.