A button cell used in watches function as following.

${\mathrm{Zn}}_{\mathrm{s}}+{\mathrm{Ag}}_2{\mathrm{O}}_{\left(\mathrm{s}\right)}+{\mathrm{H}}_2{\mathrm{O}}_{\left(\mathrm{l}\right)}\rightleftharpoons 2{\mathrm{Ag}}_{\left(\mathrm{s}\right)}+{\mathrm{Zn}}_{\left(\mathrm{aq}\right)}^{2+}+2{\mathrm{OH}}_{\left(\mathrm{aq}\right)}^{-}$

If half cell potentials are

$$\begin{gathered} {\mathrm{Zn}}_{\left(\mathrm{aq}\right)}^{2+}+2{\mathrm{e}}^{-}\to {\mathrm{Zn}}_{\left(\mathrm{s}\right)};{\mathrm{E}}^0=-0.76\mathrm{V} \\ {\mathrm{Ag}}_2{\mathrm{O}}_{\left(\mathrm{s}\right)}+{\mathrm{H}}_2{\mathrm{O}}_{\left(\mathrm{l}\right)}+2{\mathrm{e}}^{-}\to 2{\mathrm{Ag}}_{\left(\mathrm{s}\right)}+2{\mathrm{OH}}_{\left(\mathrm{aq}\right)}^{-},{\mathrm{E}}^0=0.34\mathrm{V} \end{gathered}$$

The cell potential will be