4 ms·

A water/gravity battery comes to mind. Definitely not the answer you are looking for, but an answer none the less.

• enchiridion 5y ago
  Depends on your definitions. Is the water pumped considered part of the battery before it’s elevated?
  • jermaustin1 5y ago
    The pumping of the water would be "charging" the barrel of water, I guess.
    • einpoklum 5y ago
      I'm sure this will work great for powering an aircraft, too. You could just let it all hang from an anchor at the highest point in the battery :-P