Don't do it.
Once upon a time it was relatively safe and easy and common. I've used lead from only 1 battery though sometime in the 1960's.
The acid is not the issue.
The introduction of maintenance free later more or less sealed batteries included changes in the lead alloy. It's not safe and it doesn't give much lead after jumping through hoops to do it safely. Currently used batteries typically have some turn in value some have a recycling fee built in to new battery sales and other such that will allow buying as much good alloy as junking out the battery will ever produce.
