This post suggests that after a few minutes the Pencil enters into sleep mode. An information that isn't available ANYWHERE. I discovered right now something interesting:
Speaking of battery, once the 1st gen Pencil it's attached to the charging adapter and a lightning to USB cable it keeps trying to broadcast a signal. So even if I turn bluetooth 100% off this will happen.
Could this be due to this Pencil trying to broadcast to the iPAD's widget the current battery levels? Since there's no off switch I find odd that only recharging would make it emit RF radiation. The act of recharging shouldn't trigger this.
I recorded a video a few minutes ago which show the Pencil is broadcasting no matter what (see above). I have removed it from the cable and charging adapter, and also told the IPP 10.5 to unpair...
Should I wait for the Cornet meter to stop picking a signal? I hope this happens otherwise it's the reason why the battery decreased 21% in 2 days while in my drawer and bluetooth has been totally disabled in the iPAD.
The fact there's no off switch in it and it keeps on 24/7 broadcasting a signal is a stupid design. With the Airpods I believe they continue to broadcast once are outside their charger case, but that was explained by Apple in this message:
This is an engineering tradeoff. If we were to stop all paging and advertising while the buds are sitting idle on your desk, any time you picked them up and placed them in your ear, we’d take a few seconds to connect. We prioritize the more often seen user situation in which the user leaves the buds out only when they intend to use them relatively soon after.
Edit: it's been at least 1 hour since I recorded this video and the 1st gen Pencil is still broadcasting from my drawer.
Update: I discovered how to stop with the broadcasting: I activated bluetooth and paired minutes ago. Then used with Notability. After I disabled bluetooth from iOS settings the meter stopped picking a signal while close to it. So apparently if we disable twice it stops wasting battery in idle? It seems once wasn't enough.
I wonder how that works with the 2nd gen.
2nd update: now it's going into sleep mode (no broadcast) after I disable BT just once, even after it's being plugged into the adapter and cable to be recharged. This was probably a temporary error. I am sure it's a flaw in it that will waste battery even when idle.
This was probably corrected in the new Pencil.