NOVELTY - A hybrid energy storage system (10) comprises first energy storage device (12) including a battery having impedance for providing constant power output; and second energy storage device (14) linked to first storage and including high power electrochemical double layer capacitor (EDLC) for providing intermittent bursts of high power output over 1.5-3.5 volts, where an operation rating of the second energy source is within a temperature range of 75-330 degrees C while exhibiting leakage current less than 1 amp/l of volume over the range of operating temperatures and at voltage of up to 3.5 volts.    USE - As hybrid energy storage system (HESS) for providing at least one of high power and pulsed power from a power supply (claimed); as electrochemical double-layer capacitors; and as battery-capacitor hybrid energy storage system for high temperature applications.    ADVANTAGE - The system efficiently meets certain required specifications in total energy capacity, power handling capability and physical size and weight. The system provides energy source which is capable of providing a suitable combination of total energy capacity, power handling capability per unit weight and volume and that operates at high temperature without the need for a high-rate lithium cell. The hybrid energy storage system (HESS) effectively buffers pulses every 5 seconds without discharging the battery more than 1% per hour. The HESS achieves lower weight and volume compared to the BESS while incorporating a low-rate rather than a high-rate primary.    DETAILED DESCRIPTION - A hybrid energy storage system (10) comprises a first energy storage device (12) including a battery having an impedance for providing a constant power output; and a second energy storage device (14) linked to the first energy storage and including a high power electrochemical double layer capacitor (EDLC) for providing intermittent bursts of high power output over 1.5-3.5 volts, where an operation rating of the second energy source is within a temperature range of 75-330 degrees C while exhibiting a leakage current less than 1 amp per liter of volume over the range of operating temperatures and at a voltage of up to 3.5 volts. The battery is selected from lead-acid batteries, nickel cadmium batteries, nickel metal hydride batteries, lithium ion batteries, and/or lithium polymer batteries. The EDLC comprises: two electrodes wetted with an electrolyte, where each electrode is attached to or in contact with or coated onto a current collector and separated from each other by a separator porous to the electrolyte, where the electrodes, electrolyte and current collector contains less than 1000 parts per million (ppm) of impurities. The two electrodes, the separator and the electrolyte have a low moisture concentration. INDEPENDENT CLAIMS are included for the following:    (1) fabricating an energy storage system involving selecting a first energy storage that exhibits a high energy density; and coupling the first energy storage to a second energy storage, where the second energy storage comprises at least one electrode that comprises carbon, an electrolyte and a separator hermetically sealed within a body, where the second energy storage is adapted for operation in a temperature range of -20 to about 300 degrees C. The method further involves selecting the second energy storage, where at least one of the electrode, the electrolyte and the separator have been dried to reduce impurities in it; and selecting the second energy storage, where assembly has been performed in an atmosphere of less than 50 parts per million of moisture; or selecting the second energy storage that comprises at least one of less than 500 parts per million of moisture and less that 1000 parts per million of impurities; and    (2) providing at least one of high power and pulsed power from a power supply, involving selecting a power supply comprising a first energy storage device exhibiting an impedance for providing a constant power output; and a second energy storage device linked to the first energy storage, where the second energy storage includes an electrochemical double layer capacitor (EDLC) for providing intermittent bursts of high power output over a range of about one and one half volts to about three and one half volts, where an operation rating of the second energy source is within a temperature range of 75-330 degrees C while exhibiting a leakage current less than one amp per liter of volume over the range of operating temperatures and at a voltage of up to about three and one half volts; and discharging the power supply.    DESCRIPTION OF DRAWING(S) - The figure shows block diagram of battery-ultra capacitor hybrid energy storage system.    Battery-ultra capacitor hybrid energy storage system (10)    First energy source (12)    Second energy source (14)    First resistor (16)    Second resistor (18)