iPencil for iPad not charging

First, compatibility. Here is Apple’s definitive compatibility list for Apple Pencil and iPad:

Apple Pencil compatibility - Apple Support

The first and second generation Pencil use an entirely different pairing and charging interface. 

The second generation Pencil can only be used with iPad models that have the magnetic/inductive dock that is exclusively designed for the Pencil. Charging and pairing is controlled via the iPad magnetic dock.

The first generation Apple Pencil uses the physical Lightning port of the Pencil and host iPad for both pairing and charging the first generation Pencil. The first generation Pencil can also be charged using an inline charging adapter and the iPad’s Power Adapter. This pencil can only be used with compatible iPad models that have a Lightning connector; with the sole exception of the new iPad10, requiring a special adapter, iPad models that feature a USB-C port lack any means by which to pair with a first generation Pencil.

iPad models with a USB-C port also support the new USB-C Pencil (iPadOS 17.1 or later required).

In summary, the Apple Pencil models are not interchangeable - and can only be used with the iPad that has appropriate internal hardware.

Assuming that your Pencil is compatible with your iPad, these support pages may be helpful with pairing and use of the Pencil with your iPad:

Connect Apple Pencil with your iPad - Apple Support

Charge your Apple Pencil and check the battery - Apple Support

If you continue to experience difficulties, here is one of the better troubleshooting guides:

https://appletoolbox.com/apple-pencil-not-working-heres-our-troubleshooting-guide/

Be aware that if your Pencil has been set-aside for an extended period, unused and uncharged, the Pencil battery may have been damaged through deep discharge. In common with all Li-ion batteries, they must always have some level of charge.

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. 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.

Gentle warming of the Pencil (such as placing on a hot water radiator), prior to attempting charging of the Pencil, can sometimes resurrect a dead Pencil battery.

For much newer design iPad models, without a Home button, try the new simple hard reset/forced restart procedure for the new 2018-2022 iPad Pros, 2020/21 iPad Air 4 and 5, the 2021 iPad Mini 6 and the new 2022, 10th gen base models,

1. Press and release the volume button closest to the top Power button

2. Then immediately ( and quickly ) press and release the volume button farthest from the top Power button.

3. Then, press and hold the top single sleep/wake/power button You will see the Slide to Power off button, but keep on holding down the power button until you see the Apple logo, then let it go.

Once you have performed all the steps, wait for a few seconds and your 2018-2022 iPad will boot up completely to the iPad’s Lock screen.

Tap, read and follow this Apple support link below.

Force restart iPad - Apple Support

Best of Luck to You!