The Collaborative International Dictionary
Water battery
Water battery \Wa"ter bat"ter*y\
(Elec.) A voltaic battery in which the exciting fluid is water.
(Mil.) A battery nearly on a level with the water.
Wikipedia
Water battery
A water battery is a water based battery developed in 2014 by researchers at University of Southern California. It is capable of large energy density, tough cycle durability and costs 10 times less than comparable lithium ion batteries.