When the lead storage cell provides current (1.e., during discharge), spongy lead (Pb) is oxidised to Pb2+ ions and negative charge accumulates on lead plates. The‌Pb2+ ions so formed combine with SO42− ions from H2SO4 to form insoluble PbSO4. The overall oxidation is the sum of these two processes. ‌Pb(s)→Pb(aq)2++2e−‌‌ (oxidation) ‌ ‌Pb(aq)2++SO4(aq)2−→PbSO4(s)‌ (precipitation) ‌ ‌Pb(s)+SO4(ag)2−→PbSO4(s)+2e−‌ (Overall oxidation) ‌