(EP948796-A1)      A low volume, high capacity storage device is claimed comprising an electrolytic capacitor having at least one anode layer, at least one cathode layer and a spacer comprising a mechanical separator means having a thickness of no greater than about 35 m and an elastomeric electrolyte disposed therebetween and comprising a crosslinking agent and at least one salt in an ionically conductive carrier of high solvation power, where the separator means is impregnated with the electrolyte.    Also claimed is a spacer for use in a storage device as above comprising a mechanical separator and elastomeric electrolyte as above.    Also claimed is forming an elastomeric electrolyte for use in a storage device as above.    Also claimed is construction of storage device as above comprising: (a') as above; (b') assembling a capacitor element by disposing a spacer as above between at least one anode layer and at least one cathode layer; (c') impregnating the capacitor element with the liquid mixture; and (d') as (c) above.    Preferably the crosslinking agent is a difunctional monomer selected from divinyl, diacrylate and dialkacrylate compounds, particularly tetraethyleneglycol diacrylate. The salt is selected from the alkali metal, alkaline earth metal, transition metal, ammonium, substituted ammonium, lead, tin, zinc and cadmium salts of mono-, di-, tri- and tetra-basic acids, preferably it comprises a mixture of substantially equal molar concentrations of ammonium adipate and ammonium glutarate.    USE -   These storage devices are suitable for use in implantable biomedical electronic devices such as cardiac pacemakers and defibrillators.    ADVANTAGE -   These electrolytic capacitors use a conventional mechanical separator of substantially reduced thickness. They are inexpensive to manufacture and of reduced volume. The separators exhibit higher strength and stability than those of prior art. The capacitor also shows an improvement in energy density, internal resistance and capacitor life.