I have poured/painted/sold probably over 10,000 jigs in the last 2 or 3 years. My buddy and I do it together as a hobby that pays for itself.
Anyway, we get 90% of our lead from the local Walmart tire shop. Cheaper for them to "give" it to us then to have it picked up by the recycler. We melt the tire wieghts down in an old cast iron frying pan, we welded on a extra hanlde on the opposite side, so two guys can lift it and pour into our molds. We always, always, always wear respirators, thick gloves, saftey glasses, and old grubby clothes to do this work. And we always do it out in the open in a back yard or drive way.
In my past experience DO NOT USE old batteries for lead. Just way to much mess and it can be very dangerous. On a couple occasions we have had the termials cause "explosions" in the lead pot. Probably due to an air pocket or maybe some sort of chemical reaction from left over residue of some sort. You better off sticking to pure lead or tire weights. Plus I prefer tire weights because the lead used for tire weights is harder than pure lead. Which is nice if your boucing jigs off rocks, gravel etc.