I'd never heard about metal-air batteries, but they are supposed to be lightweight but non-rechargable.
Not sure how this tech compares to super-capacitors.
Anyways, now they have a longer shelf life:
https://www.sciencenews.org/article/these-fragile-futuristic-batteries-run-longer-little-oil
Each aluminum-air battery cell contains two electrodes, an aluminum anode and a cathode, separated by a liquid called an electrolyte. Oxygen molecules sucked from the air enter the cathode, where they react with electrons and aluminum particles that flow through the electrolyte from the anode, releasing energy to power electronics. Unfortunately, when the battery is on standby, the watery electrolyte eats away at the aluminum anode.