And the batteries which don't actually gain mass as they discharge. "Metal-air batteries", or a "metal-air electrochemical cell", as Wikipedia prefers to call

And the batteries which don't actually gain mass as they discharge. "Metal-air batteries", or a "metal-air electrochemical cell", as Wikipedia prefers to call it, rely on atmospheric oxygen as the cathode which is bound to the battery during discharge, increasing total mass. <https://en.wikipedia.org/wiki/Metal%E2%80%93air_electrochemical_cell https://en.wikipedia.org/wiki/Metal%E2%80%93air_electrochemi...>