One embodiment of the present subject matter includes an apparatus which includes a capacitor stack, including at least one substantially planar capacitor electrode, a case having a first opening and a second opening, the first opening sized for passage of the capacitor stack, the second opening defined by walls having a first thickness, a cover substantially conforming to the first opening and sealingly connected to the first opening and a plate substantially conforming to the second opening, the plate sealingly connected to the second opening, the plate having a second thickness which is approximately greater than the first thickness of the walls defining the second opening, wherein the capacitor stack is disposed in the case.