For charging of lead storage battery cell reaction is 2PbSO4( s)+2H2O(l)→Pb(s)+PbO2( s)+2H2SO4(aq) At anode PbSO4 reduced back to Pb and at cathode PbSO4 oxidised back to PbO2.
$\begin{aligned}
& \because \quad \mathrm{x}_1=+2, \mathrm{y}_1=0 \
& \mathrm{x}_2=+2, \mathrm{y}_2=4
\end{aligned}$