1. A method of managing power within an aircraft electrical system, the aircraft comprising a generator driven by a gas turbine engine for a supply of electrical power to the system, wherein the generator and electrical system are connected to a common energy store, the method comprising: determining or receiving predicted electrical energy demands of the system over at least a portion of a flight; determining or receiving predicted thrust demands for the gas turbine engine over the at least said portion of the flight; defining a plurality of time periods within at least said portion of the flight; determining a desirous rate of charge and discharge of the common energy store for each time period based upon the predicted thrust demands and the predicted electrical energy demands over said time period; and controlling a rate of charge of the common energy store during at least said portion of the flight in accordance with the determined desirous rate of charge and discharge for each time period.