Unfortunately car batteries contain mostly lead oxides, diluted sulfuric acid and plastic. You can’t just melt them into bullets. I cast my own bullets where I live it is starting to get more difficult to get scrap lead... mostly because lead tire weights have now been banned for a couple of years.
“Unfortunately car batteries contain mostly lead oxides”
Nope, not true. No lead oxides... Lead sulfates. The plates in a lead acid battery are a lead grid filled with sponge lead. The sulfur goes between lead sulphate and sulfuric acid, depending on the charge level.
Take one apart and melt it down. You get most off the weight as lead...
I collect tire balancing weights. If you see a car on the highway with a bouncing tire or two. Think of Conspiracy Guy.