apple pencil 2 will not charge - is at the moment 0%

You already have a truthful assessment of your Apple Pencil.

The tiny internal Li-ion battery is susceptible to permanent/irreversible damage through being left discharged for long periods. Even some “new” pencils can exhibit signs of failure out-of-the-box if they are “old stock”. It is essential that if you have an Apple Pencil that you charge it regularly - whether used or not - so as to protect the battery from deep-discharge.

Do not allow a pencil to remain in low-charge state for any period of time - as the internal battery will fail, rendering the Pencil useless. Setting aside an unused Pencil, for extended periods, is a recipe for premature death of the Pencil battery.

If the Pencil Battery has failed, the only remedy is to replace the Pencil; an Apple Pencil cannot be repaired. If the battery has failed and your pencil is within its one-year warranty, you should look to having it replaced by your retailer or at an Apple Store. Otherwise, the Pencil should be returned to Apple for responsible recycling.

A suitable warning is indeed an omission within Apple’s documentation.

Unfortunately, the Apple Pencil does not have an on/off switch with which to isolate the battery when unused. The Pencil does have a “soft-off” (shipping) condition that can be triggered - but this procedure is, again, not documented.

Whilst idle, the Pencil will reduce its power usage to its minimum; whilst minimal, a “sleeping” pencil is always consuming some power from its tiny battery. In the “shipping” state, battery charge depletion is reduced almost to that of natural self discharge of the battery.

Apple do invite constructive feedback and comment via their product feedback pages. I don’t recall seeing a feedback page for the Apple Pencil, however, the iPad page is perhaps the most appropriate to offer feedback regarding practical aspects of Apple Pencil:

Feedback - iPad - Apple