The first generation Pencil is charged and paired from iPad10 using the iPad charging cable - and an Apple USB-C to Apple Pencil Adapter:
New first generation Pencils now ship with this special adapter in the box along with the Pencil. However, some older stock purchased from retailers may lack the USB-C to Lightning adapter - and may instead have an older Lightning to Lightning Adapter.
For owners of older first generation Pencils, or for “old stock” new Pencils, the new special adapter can be purchased directly from Apple as an accessory.
https://store.apple.com/xc/product/MQLU3ZM/A
As such, if purchasing a new first generation Apple Pencil to accompany an iPad10, you might be best advised to visit an Apple Store or Apple Authorised Retailer that has a high-turnover of stock - and ensure that the Pencil box indicates that the correct adapter is included.
If necessary, open the box in the Store and check that the USB-C/Lightning adapter is present - noting that the older Lightning/Lightning adapter looks very similar to the USB-C/Lightning adapter.
Assuming that you have the correct adapter and charging cable, this support page may be helpful with pairing and use of the Pencil with your iPad:
Connect Apple Pencil with your iPad - 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 now be irretrievably 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.
