That's an interesting question. As you say, it depends on definitions. I would say that some betavoltaic devices would qualify, and perhaps some phase-change s

That's an interesting question. As you say, it depends on definitions. I would say that some betavoltaic devices would qualify, and perhaps some phase-change stuff that I can't recall right now. Supercapacitors are essentially batteries but I seem to recall they actually do ion exchange as well.