“Lead is very common in car batteries, but you really do not want to melt them down, there are a lot of nasties in there that will kill you pretty quickly. I make sinkers and all manner of lead fishing stuff, and i will not touch car batteries for this purpose. Find a different source!”
Right you are, but we are talking desperation/survival. In such situations, we will be doing plenty of ill-advised things.
Effing with batteries for lead will kill you faster than whatever it is you plan to shoot at, you’ll be taking yourself out. Seriously, even in desparation, it’s a bad, bad idea. Even in an extremely desperate situation, it’s still a bad idea.