[Anaraxes]

I don't understand the passive / active distinction. A capacitor stores energy in an electric field. A battery stores electrical energy as chemical energy. If anything, the battery seems the more "active" of the two in that more has to happen to get electricity back out. But they both have to change something about their state.

"Accumulator" is a general term for something that stores energy; by that definition, both batteries and capacitors are types of (electrical) accumulator. I've also seen that term used for non-electrical energy storage, as in hydraulic systems, so it seems the broadest of the three, and thus appropriate enough either for purposes of the OP or of Doc Smith.