The energies of the solid reactants in the lead-acid battery are calculated
ab initio using two different basis sets at non-relativistic, scalar
relativistic, and fully relativistic levels, and using several
exchange-correlation potentials. The average calculated standard voltage is
2.13 V, compared with the experimental value of 2.11 V. All calculations agree
in that 1.7-1.8 V of this standard voltage arise from relativistic effects,
mainly from PbO2 but also from PbSO4