The present subject matter includes one embodiment of an apparatus, comprising: a battery including a plurality of flat battery layers disposed in a battery case, the battery case having a planar battery surface which has a battery perimeter; and a capacitor including a plurality of flat capacitor layers disposed in a capacitor case, the capacitor case having a planar capacitor surface which has a capacitor perimeter, the capacitor stacked with the battery such that the planar battery surface and the planar capacitor surface are adjacent, with the capacitor perimeter and the battery perimeter substantially coextensive; a hermetically sealed implantable housing having a first shell and a lid mated to the first shell at a first opening, the first opening sized for passage of the battery, the capacitor, and the programmable electronics, wherein the battery and the capacitor are disposed in the hermetically sealed implantable housing.