Sell the battery and buy lead.
Getting lead from batteries is not cost effective. I've tried it. A ton of work, the acid eats your cloths, boots, and is dangerous. Not to mention the time involve, both in getting the lead and cleaning up the mess.
One session, I figured out the cost. For what I had to pay for a replacement shirt, jeans, I could have bought a heck of a lot of bullets.
No sir, it ain't worth it.
I bet, if your shop is anything like mine, you can find enough scrap iron, brass, batteries, etc. to take to the scrap yard, and trade for enough casting lead to do your winter casting.
Heck, talk to your neighbors, I bet they have a lot of scrap they would love for you to haul off.
Kind of un-related, but it points out what I'm talking about. I had a neighbor kid who turned 16 and got his driver's license. Barrowed his parents truck and trailer and went through the valley checking with neighbors to see if they had any scrap iron 'n suck that they needed hauled off.
Kid paid for his gas, and got enough money to buy an old used car and pay his first year's insurance.
If this kid can do that, we can do enough to buy a bit of casting lead, without the danger and headache of busting up batteries for the lead.
CPT USAR Ret
USAMU Sniper School Oct '78
Distinguished Rifle Badge 1071