A battery powered pump takes up just as much room as a plug in pump, and uses tubing. The only thing missing is a cord and plug. And it will only last a few hours. So unless I am misunderstanding your question, it would not be any "improvement" over a regular air pump.
Or are you looking for an airstone alone that is battery powered? I have never seen anything like that. And if they do exist, you would still need tubing to get the air down to the stone.....and put batteries under water...