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Hey there @Hornblende
Thanks for stopping by.
If you went through the details of the article, it is not really relevant to the amount of Voltage, it drills down to the actual amps/electrical circuit, combined with the resistance of the recipient's body.
In such situations, 12V batteries can cause some risk (12V being a car battery), and even one delicate experiment with a 9V battery proved fatal as explained in the post.
Feel free to check out the references if in need for further explanations
Thanks again!