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

$$\ce{Zn + Cu^2+ -&gt; Zn^2+ + Cu}$$

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.