Do not, repeat do not, try to melt down batteries for the lead.
First of all, the process gives off Arsine and Stibine gases, which are uniformly fatal when inhaled. Battery processors have methods in place to deal with this. Second, the yield of usable lead would be very low as the acid over time has converted a lot of it into sulfates and other products. There are many ways to get lead besides wheel weights. Check with your local scrap yards, advertise on Craig's List, buy from Rotometals.com, prices really aren't that bad and you know exactly what you're getting. Goat