Phys.org- Batteries that "drink" seawater

https://phys.org/news/2017-06-batteries-seawater-power-long-range-underwater.html

"Now MIT spinout Open Water Power (OWP) aims to greatly improve the range of unpiloted underwater vehicles (UUVs), helping them better perform in a range of applications under the sea.

Recently acquired by major tech firm L3 Technologies, OWP has developed a novel aluminum-water power system that's safer and more durable, and that gives UUVs a tenfold increase in range over traditional lithium-ion batteries used for the same applications."