An electrical system for an aircraft, comprising: one or more energy sinks, wherein each energy sink of the one or more energy sinks comprises a load; and a hybrid energy storage system, comprising: one or more primary energy sources that are coupled to the one or more energy sinks and supply power to the one or more energy sinks, wherein each primary energy source of the one or more primary energy sources comprises: an energy storage unit that stores electrical energy and supplies power at a predetermined voltage range, and an electrical energy source management unit that collects sensor data from the energy storage unit; a secondary energy source that is coupled to the one or more primary energy sources and adapted to supply power at a variable output voltage to the one or more primary energy sources; and a secondary energy source control unit that receives the sensor data from the electrical energy source management unit and sends command signals to the secondary energy source to control the variable output voltage based on the sensor data, wherein the secondary energy source control unit is adapted to directing the secondary energy source to provide the variable output voltage at a value that is smaller or greater than at least one output voltage of all of the one or more primary energy sources when all of the one or more primary energy sources are working normal and are contributing to supply the respective one or more energy sinks. one or more energy sinks, wherein each energy sink of the one or more energy sinks comprises a load; and a hybrid energy storage system, comprising: one or more primary energy sources that are coupled to the one or more energy sinks and supply power to the one or more energy sinks, wherein each primary energy source of the one or more primary energy sources comprises: an energy storage unit that stores electrical energy and supplies power at a predetermined voltage range, and an electrical energy source management unit that collects sensor data from the energy storage unit; a secondary energy source that is coupled to the one or more primary energy sources and adapted to supply power at a variable output voltage to the one or more primary energy sources; and a secondary energy source control unit that receives the sensor data from the electrical energy source management unit and sends command signals to the secondary energy source to control the variable output voltage based on the sensor data, wherein the secondary energy source control unit is adapted to directing the secondary energy source to provide the variable output voltage at a value that is smaller or greater than at least one output voltage of all of the one or more primary energy sources when all of the one or more primary energy sources are working normal and are contributing to supply the respective one or more energy sinks. one or more primary energy sources that are coupled to the one or more energy sinks and supply power to the one or more energy sinks, wherein each primary energy source of the one or more primary energy sources comprises: an energy storage unit that stores electrical energy and supplies power at a predetermined voltage range, and an electrical energy source management unit that collects sensor data from the energy storage unit; an energy storage unit that stores electrical energy and supplies power at a predetermined voltage range, and an electrical energy source management unit that collects sensor data from the energy storage unit; a secondary energy source that is coupled to the one or more primary energy sources and adapted to supply power at a variable output voltage to the one or more primary energy sources; and a secondary energy source control unit that receives the sensor data from the electrical energy source management unit and sends command signals to the secondary energy source to control the variable output voltage based on the sensor data, wherein the secondary energy source control unit is adapted to directing the secondary energy source to provide the variable output voltage at a value that is smaller or greater than at least one output voltage of all of the one or more primary energy sources when all of the one or more primary energy sources are working normal and are contributing to supply the respective one or more energy sinks.