Durable high density power supply

A packaged power supply (10) is provided having a rigid enclosure surrounding an electrical energy storage device such as an electrochemical cell (32). Cells used are of a type that incorporate stacked planar electrodes sealed in a flexible foil or plastic laminate envelope (52) and is otherwise unprotected. Other similarly unprotected energy storage devices such as planar capacitors are alternatively used. The invention has particular advantages when used with planar electrochemical cells such as lithium-ion, lithium-polymer, lithium-sulphur and other similar cells having planar lithium based anodes. The enclosure uses thin metal covers (12, 14) to surround the cell or cells to provide physical protection from external forces and to act as a fire barrier to isolate high energy lithium based electrodes. The thinness of metal covers and the low volume construction of the enclosure minimizes the enclosure's adverse impact on overall energy density.