"Um..." He'll never learn, apparently. "Well, your engine here would count as a generator. That just means a thing that makes power. I'm just thinking of a kind that works by agitating a certain metal alongside a magnet." Is magnet okay? He's pretty sure magnetism is naturally occurring, but Armin doesn't even know about shellfish, so if his very limited experience didn't happen to overlap any sources of particular iron ores. "Nevermind. It makes power, the same as burning fuel. There are just... better ways to do that. Including some batteries, which are just any object that you can extract power from, usually from a chemical or radioactive reaction. Just... a different power source. Something lighter and longer lasting, and less polluting." He's from a world of all-green energy. That people fighting Titans wouldn't really care about a bit of smoke in the air doesn't occur to him.