Redox batteries

I am currently trying to define what the appropriate battery would be for a hybrid boat. I found information on Vanadium batteries, that apparently are close to commercialization. Their biggest drawback is apparently the low specific energy, but this is not very critical on a boat. I also read about Cerium that could provide a higher energy density.
Does someone know about these? What is their future? Are the claimed advantages of Vanadium batteries true?
In short, I would like to discuss the topic in all its aspects, including hazard and ecologic risk.
For those who have no documentation but are chemists - which i am not - I can supply them with information I got by writing to a company that is currently developing a vanadium battery.
Jean-Marc
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