A capacitive battery cell (11) comprises: (a) a pair of conductive, hydrophilic electrodes (16,16) which can be charged to capacitively store electrical energy; (b) a separator (17) interposed between, and in contact with, the electrodes; (c) an aq. electrolyte wetting the separator and electrodes; (d) a pair of electrically conductive supports (18,18) substantially impervious to the electrolyte superposed on each electrode on the outsides, opposite the separator; and (e) a seal (19) that retains the electrolyte between the electrodes.    Also claimed is a battery as above comprising a plurality of cells, where electrical connections connect the cells in series, and positive (12) and negative (13) terminals connect to the endmost cells in the series.    Also claimed is a dual battery including a main battery and a reserve battery connected in parallel to common positive and negative terminals and electrical connections that draw power selectively from the two batteries under different conditions.    Also claimed is a process for producing the battery comprising: (a) forming a dry mixt. of plastic and a particulate, electrically conductive material; (b) rolling the mixt. into a sheet under conditions effective to fibrillate the plastic to for a fibrous network that retains the conductive particles; (c) laminating the sheet with a conductive support to form a second support and electrode; (d) repeating steps (a) to (c) to form a second support and electrode; (e) interposing a porous separator between the first and second electrodes; (f) forming a seal about a space between the electrodes, which contains the separator, and filling the space with an aq. electrolyte; (g) deaerating the electrolyte; and (h) closing the seal to render the space air-tight.    USE -   Used to deliver a short, high power pulse discharge in, e.g., battery systems for motor vehicles.    ADVANTAGE -   Draws power selectively from the main or reserve batteries to aid starting at a cold temp. or when the main battery charge is low.