Abstract: A method for controlling electrical connection of at least two battery packs (202, 203) of an energy storage System (200) of a vehicle (201) to a common load during operation of the vehicle, each one of the battery packs being connectable to the load via at least one respective switching device, the method comprising: —receiving measurement data relating to current operating conditions of the energy storage System, —based on at least the measurement data, estimating at least one battery state of each one of the battery packs, wherein said at least one battery state is at least one of an open circuit voltage and a state of charge, —based on the estimated at least one battery state of each one of the battery packs, controlling electrical connection of each battery pack to the load via the at least one respective switching device.