Why is there a discrepancy between predicted and nominal voltages of alkaline batteries?

According to [Wikipedia](https://en.wikipedia.org/wiki/Alkaline_battery), the sum of standard reduction potentials for the half reactions for alkaline battery yield $\pu{1.43 V}:$


$$\begin{align}
\ce{Zn(s) + 2 HO–(aq) &-> ZnO(s) + H2O(l) + 2 e–} &\quad E^\circ &= \pu{+1.28 V} \\
\ce{2 MnO2(s) + H2O(l) + 2 e– &-> Mn2O3(s) + 2 HO–(aq)} &\quad E^\circ &= \pu{+0.15 V} \\
\hline
\ce{Zn(s) + 2 MnO2(s) &-> ZnO(s) + Mn2O3(s)} &\quad E^\circ &= \pu{+1.43 V}
\end{align}$$


However, the reported voltage of Duracell or other alkaline batteries is $\pu{1.5 V},$ and the actual zero-load voltage of a new alkaline battery is measured up to $\pu{1.65 V}.$ Why?


