The Digital Pen 2 is powered by batteries, specifically an AAAA battery, contrary to Digitec's answer below.
Unfortunately, this is also incorrectly stated in the description, please correct @digitec

Not serious that the pen now comes with a battery

The Lenovo Precision Pen 2 (laptop) with product ID GX81J19854 is powered by a lithium-ion polymer battery and can be charged via a USB-C cable. No batteries are required as the battery is integrated in the pen.