PbO2 (s) + Pb (s) + 2 H2SO4 (aq) → 2 PbSO4 (s) + 2 H2O (l)
This is an oxidation-reduction (redox) reaction:
Pb0 - 2 e- → PbII (oxidation)
PbIV + 2 e- → PbII (reduction)
Pb is a reducing agent, PbO2 is an oxidizing agent (synproportionation (comproportionation)).