Be extremely leery of using car batteries as a lead source for boolits. The lead contained in them is very impure with a high percentage of lead oxide which is the most dangerous form of lead. There are also other contaminates that make it less than desirable as a casting alloy. Not saying it can't be done just that it is suboptimal. Also soaking plates in vinegar to neutralize acid will not work. It may dilute the acid but since vinegar is itself an acid it can't neutralize acid. A better solution to use would be baking soda or some other base.
I knew of a guy that just built a bonfire around a pile of old automotive batteries and lit her up. He'd go back later and retrieve the clumps of lead from the ashes. On a side note, nothing will probably grow on that spot of ground for the next century or two. :devilsidesmile: