I would be careful about lead having gotten into that soil. Lead-acid batteries work by lead dissolving into the acid (releasing electrons). When you recharge the battery, some of that lead precipitates back onto the electrodes.
But there is always some lead in the acid.
You really, really do not want to eat anything that has absorbed much lead. Ask the people in Flint Michigan! lead is truly "toxic" toxic, not "I don't like to use chemicals" toxic.
I would send the soil to some landfill rather than wonder about residual lead levels.
But if you limit your concern to the acidity of the sulfuric acid, lime plus weeks of rain would reduce that acidity.
Personally, I don't worry about some toxin that will TELL me if I'm exposed to an effective concentration. Sulfuric acid will either dissolve my shoe-soles or not, and burn my skin and lungs or not. If not, I'm not worried. If it does, I will know exactly how much damage was done. The pain is a clear indicator of exposure! No worries, mate!)
But lead is a persistent, cumulative nerve toxin. It will damage my brain and nerves and maybe some enzymes subtly or seriously, and I might not know until years later. I could absorb a few micrograms (or, God forbid, milligrams) per year if any vegetables grew near that patch or dust blew up from it. THAT, I worry about!
P.S. When you sell the place, in theory you're required by law in most states to reveal anything you know about toxic chemical spills. How much nicer to be able to say "But I dug up all that soil and sent it to the landfill one gallon at a time ".
