In electric circuits, the charge carriers are electrons, which are already inside the wire itself. The battery doesn’t add extra electrons to the circuit to make it go… the electrons inside the wires are already there. The battery provides an electric potential difference that signals the electrons to start moving, and this signal travels at the speed of light (or close to it), and then the electrons start moving (quite a bit slower than the speed of light). This means that electrons don’t have to start at the battery and them go all the way to the light before the light bulb lights up, because the electrons inside the filament itself are the ones that start glowing when they get the signal to start moving.
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