I will go on record as one that does not agree with either this thread or the reported results on this experiment. To be blunt it gives the wrong ideas. One should simply take their spent battery in and get the $12 core charge and apply this to purchasing clean good lead.
The whole idea that one can or even should try to melt down batteries is bad to the bone. Leave them to hell alone. You will understand this when you observe what can happen when trying to melt down batteries. I've seen explosions and the shrapnel a battery can throw should in itself be enough for those with a mental capacity over that of a stream rock.
Just leave then to hell alone.