Water battery : A voltaic battery in which the exciting fluid is water.

Water battery : A battery nearly on a level with the water.

Example:


Taxonomy
battery, Water Battery, the Japanese, a battery, drinking water, United States, Blanton, President & CEO, battery technology, Aqua Power, product, Power Battery, AA, shelf life, Power Systems, drops of water, new type, battery operated.

Defination from the web:
battery has a small hole in the bottom that you fill with a small amount of water. ... You can fill the battery by just dropping it into a glass of regular drinking water. ...