Is it possible for a 12 volt car battery to shock you enough to cause injury or death?
No. The sulphuric acid in an automotive battery presents a safety hazard. A battery can also vent hydrogen gas, which is flammable. Since a battery can supply several hundred amps to crank an engine, shorting the positive and negative terminals is not the brightest thing to do. Don’t try to short the battery with a wire or a wrench, because it will violently short out and can explode.