Yeah, it's annoying there is no purity spec on the battery acid, but in all likelihood, it's pretty pure. One could always test it.

I mean I bet nitric acid would work great for that purpose, it's just a bit more expensive and harder to get in some places, as you mention. It's definitely commercially available in the USA though.

Duda diesel has it: https://www.dudadiesel.com/search.php?query=nitric

Duda also has sulfuric which is likely higher purity, but you seemed to express some concerns about working with corrosives.

I'm a former chemist, so anything short of super angry chemicals like piranha solution, I'm not too phased :D