Here's a robotic fish that doesn't waste much of anything - a liquid battery powers the pumps that move the fish.
(Robotic fish uses blood for battery, locomotion)
A team from Cornell University has now demonstrated a clever twist that cuts down on the weight and density of all of this by figuring out how to get one of the materials to perform two functions. Like other soft robot designs, it pumps a fluid to cause its structure to expand and contract, powering movements. But in this case, the fluid is also the key component of a flow battery that powers the pumps. This allows them to put all the critical components on board their creation.
So what's a flow battery? Batteries operate by having different reactions that take place at their two electrodes. For something like a lithium-ion battery, the intermediaries of these reactions—electrons and ions—immediately flow from one electrode to another, and the key chemicals spend almost all their time at the electrodes. In flow batteries, the chemical reactions still take place at the electrodes, but the chemicals reside in solution, rather than being confined to electrodes.
In his 2002 story Slow Life, science fiction author Michael Swanwick writes about robot fish who help explore distant worlds:
The Mitsubishi turbot wriggled, as if alive. With one fluid motion, it surged forward, plunged, and was gone.
Lizzie switched over to the fishcam.
Black liquid flashed past the turbot’s infrared eyes.
Straight away from the shore it swam, seeing nothing but flecks of paraffin, ice, and other suspended particulates...
(Read more about the Mitsubishi turbofish)