Also, I think HCN can be scrubbed by adding a special absorptive cap onto the battery.
Cyanide could be released only at high temperatures, e.g. if the battery is opened and burned, not during normal operation, even if overcharging is not prevented, as it should.
The sulfuric acid from the traditional lead-acid car batteries is more dangerous than this.
Very much not an equal comparison.
It has the same LD50 dose as HCN. It literally _is_ just as bad. It routinely kills people on oil rigs because in lethal concentrations it immediately shuts off your nose.
How often do you hear about people getting poisoned by it from lead-acid batteries?
https://en.wikipedia.org/wiki/Hydrogen_cyanide - 107 ppm (human, 10 min)
https://en.wikipedia.org/wiki/Hydrogen_sulfide - 600 ppm (human, 30 min)
https://en.wikipedia.org/wiki/Carbon_monoxide - 4000 ppm (human, 30 min)
These are "LCLo" values from the databoxes on those pages. More easily comparable numbers may be around somewhere.
Fast charging a car/chemical weapon in your garage isn't terribly appealing.
