Battery terminals are alloyed, they are no longer pure lead. I melted down a bunch of them by themselves a while ago just to see what they are like and when hit together, the ingots ring like much harder lead. I suspect they have some zinc in them to help deter corrosion but I have no acid to test them with. I do know that if you cut them off with a hack saw and look at them from the bottom you can see a distinct separate core of different metal. Can't extract it though, I tried. It may be the harder material used for strength coated with closer to pure lead.