I have been casting bullets for over 50 years, and I have always thought about getting the lead out of car batteries. The thing is, wheel weights were always in plentiful supply, and I never went to all the work of taking a car battery apart - it just was not worth the effort.
Over all those years, I have always read that that God would immediately kill your whole family if you even thought twice about getting the lead out of batteries. Well, some folks might say that I have always been a "willful" person. Actually, if my parents were alive, they would tell you I was always something much worse than "willful," but I would not want to put their words in writing.
Last year I finally got tired of reading everybody tell how unsafe it was, and I had a big truck battery that finally went bad after 12 years of continuous use, so I decided I was going to get the lead out of that battery.
After covering myself in old cotton clothing that I could then throw away, I emptied the liquid inside by pouring it on an old tree stump I wanted to go away, and then I rinsed the battery with water about a dozen times. Using a saw, I cut the battery case into pieces so I could get to the plates inside. The cells were made up of several series of plates seperated by some kind of insulating films. The plates were not simply lead plates. Instead, they were a kind of mesh with diamond shaped pieces of something heavy filling the mesh. The cells were connected by solid lead pieces that eventually tied into the two main terminals. The "lead" mesh plates were heavy like lead, but they sure did not look like lead. The connecting pieces and terminals were obviously lead.
I collected all the "lead" mesh plates and the other lead pieces and put them in a dry place for a few weeks to insure there was no water hidden in there anywhere. I then got out my big smelting crock and started heating the "lead" mesh plates. I did it in my shed with a small fan behind me and small fan in front of me to insure a small amout of airflow in one direction - to the outdoors.
While I did manage to safely take the battery apart and smelt the heavy material inside, I did not get any real lead whatsoever other than the obvious connection pieces and terminals. All the material in those heavy "lead" mesh plates obviously were not any kind of lead I have ever used. I heated those plates for hours at very high heat, and all that happened is that the diamond shaped mesh melted while the diamond shaped pieces of metal in the mesh simply turned to something that looked like dirt. I know the material was some form of lead because it was as heavy as lead. When I put some of the "dirt" in some melted lead, the "dirt" went to the bottom of the pot instead of floating on top as dross normally would.
Whatever it was, it was not something I could use to make bullets. I guess I could have set the acetylene torch to it to see if it would melt if I got it hotter, but I had already spent more time and effort on the project than it was worth.
My conclusions were that I had no idea of what the heavy stuff inside batteries was, but it sure was not future bullets. I also figured even if I had recovered usuable lead, it simply would not have been worth the effort involved - not to mention the extra risks involved. Maybe some chemist would know what form of lead compound was inside the battery, and maybe that chemist might be able to convert it into some form of usable lead, but that was way beyond my experience and capability.
I would also go so far as to say it is not even worth messing with batteries to get the very small amount of regular lead in the connecting parts and terminals. There simply is not enough lead in those parts to go to all the work of getting them out of the case.
So, that's my story, and that is why trying to get lead from batteries is not for me.