Where is the battery with a laptop?

A laptop has a battery and where is it?

If it had no internal power supply, it would not work wirelessly.

Usually yes, otherwise he would not work without external power

Hello good morning, the bottom is completely closed, it still has to be somewhere else, but where?

then the battery is built into the case and can't be changed "just like that"

Look in your user manual, there it is in it - and also some important more.