Apple Pencil Charging too slow.

How are you attempting to charge your Pencil - and with which iPad model?

A first generation Apple Pencil will charge at its fastest when connected directly to the Lightning port of its host iPad. While the Pencil can be charged using from an iPad Power Adapter, charging adapter and cable, charging will be much slower.

See:

Pair Apple Pencil with your iPad - Apple Support

The first generation Pencil is charged and paired from iPad10 using the iPad charging cable - and an Apple USB-C to Apple Pencil Adapter:

The Pencil should charge quickly when connected directly to the iPad with the charging Adapter and the USB-C cable. When charging from the Power Adapter (again using the USB-C cable and the Pencil’s Charging Adapter), charging is much slower.

If your Pencil is not charging effectively, you would be well advised to visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to test and assess your iPad, Pencil, Charging Adapter and cable(s):

Genius Bar Reservation and Apple Support Options - Apple