Abstract: A reserve, back-up battery assembly is described providing adequate voltage and power levels to replace a main battery for a limited period of time. The reserve battery assembly includes a housing, an electrolyte, an openable sealing mechanism, a plurality of pairs of anodes and cathodes, and first and second leads integrally connected to the first and second cable assemblies. The housing includes a fluid reservoir with an electrolyte solvent sealed within it, and it further includes a cell chamber containing the anodes and cathodes. The openable sealing mechanism releases the electrolyte solvent into a chute leading from the fluid reservoir to the cell chamber, and the chute contains anhydrous electrolytic crystals, for dissociation in the electrolyte solvent. The openable sealing mechanism also opens a vent passage extending between the fluid reservoir and the exterior of the housing. The anodes and cathodes may be made from Al and S, Al and AgO, or Al and MnO.sub.2, respectively.