Something I don't understand about batteries

someone explained how a zinc copper battery works but there's already something I don't understand in the beginning.


Here is the reaction this person said happens in the battery


$$\ce{Zn + Cu^2+ -> Zn^2+ + Cu}$$


I understand how $\ce{Zn}$ transforms in $\ce{Zn^2+}$ (because it gives electrons to the wire, the $\ce{Zn^2+}$ then goes in the electrolyte) But I don't understand where the $\ce{Cu^2+}$ comes from. I understand that the $\ce{Cu^2+}$ gets electrons from the wire and turns into $Cu$ but the copper electrode that is in the battery is made out of $\ce{Cu}$ not $\ce{Cu^2+}$ so where does it come from?


It comes from the first answer here: <https://physics.stackexchange.com/questions/247725/why-electrons-flow-through-a-wire-connected-to-a-battery>




We manually put Cu ions on the electrolyte, it then reacts with the excess electrons on the electrode and makes Cu atoms.


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