Just to hopefully help anyone else going down this rabbit hole like I did... I had the same problem – I left the pencil (2nd gen) uncharged for several months and when snapping it to my iPad, it would register the pencil, but say 0%.
I tried everything I could find in every thread on the issue – reseting the bluetooth connection, hard resetting the iPad, etc. Nothing worked.
I read that the small battery in the pencil completely dies beyond recovery when leaving it uncharged for too long. I was feeling mucho dismay and planning a burial of my once-neglected pencil.
And yet WAIT, that presumed dead pencil is now working... I'm honestly not sure what did the trick, but the only thing I did between it once staying 0% and it suddenly resurrecting from the deathly graves is the following:
- I released then snapped it back to my iPad several times over and over for a couple minutes.
- I then left it on my iPad with my iPad plugged into a charger overnight
- The next morning I repeated the snap on and off procedure for a couple more minutes.
- I came back to it some time later in the day and it had risen from the dead and worked perfectly
I also read someone who had luck warming the pencil by holding it in their hand for 10mins, and that was enough for their battery to wake back up and work again, so give that a try too.