The Poseidon Mk IV Discovery is a dive tank that recycles oxygen, so you can stay underwater long enough to fall in love with a mermaid and produce mutant children. Awesome, I know. Just don't go settling for a manatee like I did. The system works through the use of C02 scrubbers and oxygen cells powered via lithium-ion battery. Unfortunately the unit does not protect divers from the bends. Or the runs. Which, in my case, are a serious problem.