Apple pencil pro charging issue

If your Apple Pencil Pro (or any Apple Pencil) is set-aside for an extended period, unused and uncharged, the Pencil battery may be 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”. 

Gentle warming of the Pencil (such as placing on a hot water radiator), prior to attempting pairing/charging of the Pencil, can sometimes resurrect a dead Pencil battery. Keeping the Pencil docked with iPad, undisturbed overnight, may help with restoring normal operation.

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

For information, it is generally recommended that an Apple Pencil Pro is always docked with the host iPad whenever it is not being actively used - as this ensures that the tiny internal battery is kept optimally charged when not in use. Charging only occurs when the battery requires charge from the iPad, optimal charge being entirely automatic. An otherwise healthy Apple Pencil will suffer no negative consequences from being docked with its host iPad for extended periods.

Charge your Apple Pencil and check the battery - Apple Support

If you just received it brand new in a factory sealed container directly from Apple or an Authorized Apple Retailer, visit an Apple Store or Authorized Apple Facility with proof of purchase and let them solve your issue.