I understand how Bluetooth works.
However, if you turn OFF Bluetooth on the iPad and turn it back on, it does NOT automatically connect to the Pencil. It still has the "history" of the pairing in Bluetooth settings - but it does not re-connect automatically. You have to plug the Pencil back in to the iPad, and then it instantly connects (NOT pairs - i.e. it doesn't ask you if you want to pair with the Pencil like it does the first time you set it up).
I used my iPad yesterday afternoon without touching my Pencil for several hours, and the Pencil stayed connected and drained a significant portion of its battery. When I turned Bluetooth OFF on the iPad, the Pencil stopped draining, but then I needed to connect it physically to the iPad again to make it work after turning Bluetooth back on.