A 20 V stack of 19 supercapacitors was fabricated from titanium bipolar plates (150 x 150 x 0.1 mm3) coated on each side with carbon nanotubes and polypyrrole composite (+) and pigment carbon black (-), and microporous polymeric separators containing aqueous KCl. Internal sealing of each cell in the stack was achieved by placing a silicone rubber washer between neighboring bipolar plates. The stack was tested by high voltage cyclic voltammetry, galvanostatic charging and discharging, and electrochemical impedance spectroscopy. It approached 25 kW/kg in maximum specific power and 3.64 Wh/kg in specific energy. Performance of the stack through intermittent charging-discharging tests in a storage period of 10 months (still ongoing) remained fairly stable. For example, it exhibited almost zero decay in capacitance after 1000 continuous galvanostatic charging-discharging cycles in the first month of storage (10 V), and less than 6% loss in the seventh month (19 V). (c) 2011 American Institute of Chemical Engineers AIChE J, 2012