One embodiment includes a 
capacitor having a first 
anode stack having a first number of 
anode foils, a second 
anode stack having a second number of anode foils, where the first number of anode foils is different than the second number of anode foils. Another aspect provides a 
capacitor having a case having a curved interior surface, and first, second, and third 
capacitor modules that confront the curved interior surface of the case. One aspect provides a capacitor having one or more anodes and a 
cathode structure comprising a plurality of integrally connected 
cathode plates, the 
cathode structure having a serpentine shape, interweaving under and over each of the one or more anodes. One aspect provides a 
feedthrough assembly having an 
electrically conductive member dimensioned to extend at least partially through a 
feedthrough hole of a case of the capacitor, the conductive member having a passage therethrough. One aspect provides a capacitor having a first stack of capacitive elements a second stack of capacitive elements, wherein the first and second stacks are enclosed in separate compartments of a capacitor case that electrically isolate the electrolytes of each stack from one another. One aspect provides a capacitor case including a portion having opposing interior and exterior surfaces, with the portion having a hole; and a semi-permeable membrane adjacent the hole to regulate passage of fluids through the hole.