should i disconnect the apple pencil when i'm no longer using it?

I do and I make sure my Bluetooth is NOT being received by Pencil when it is NOT in use.

Also,

You cannot store and/or NOT use Pencils for any prolonged period of time and NOT keep them charged up to some level.

If your Pencil/s sat around unused or unopened and not kept charged up for more than a few weeks, or so, OR

EVEN LONGER, then the battery in your Pencil may have failed and is dead and you will have to purchase another

brand new Pencil or get, if still under warranty, a free replacement Pencil from Apple.

And it looks like some things about the Pencil have NOT changed in the new version 2 model, either.

Due to the “always on and active/standby” nature of the Pencil and, also, due to its very tiny rechargeable Li-

ion battery ( smaller than the eraser head on a REAL wooden pencil ), the Pencil needs to be constantly charged up to some significant charge level ALL THE TIME, even when not using the Pencil for prolonged periods of time.

The Pencil needs to be kept CONSTANTLY charged to a minimum of 5-10%, OR GREATER, all the time!

If the Pencil battery is allowed to drain down to 0% and allowed to stay in that flat condition for more than a few weeks, or so, OR EVEN LONGER, that very tiny little Li-ion battery is too small to keep at a 0% state for a long period of time and it will fail and the Pencil will be dead and you may have to “pop” for another $99/$129 Pencil, once again!

Apple only has a one-year warranty on any Apple accessory items.

You need to keep your Pencil CONSTANTLY charged up all the time, even if it is only to 10%-15% charge. It must keep some charge level in that tiny Lithium-ion battery at all times!