The patent shows that Microsoft is looking into two changes for the Surface Pen: the battery and the dock. So far, the Surface Pen has run on AAAA batteries, which has been a perfectly fine solution because the single battery used in the Pen could last a number of months and maybe even up to a year, depending on usage. However, Microsoft is at least looking into the possibility of using a rechargeable battery in the Pen.
The patent describes a stylus charger that "may take the form of a dock that holds the stylus in a particular location during charging and/or while the stylus is not being used." The dock would hold the stylus in place magnetically, and charge the device with "charging circuits" which look like rings that would work similarly to pogo pins. The question is where said dock would live.
Microsoft has previously said that it can't have future Surface Pens go inside the tablet, because the Pen is thicker than the tablet itself, but the dock appears to be a separate accessory that would need to connect to the Surface in some way. Obviously, Microsoft is trying very hard to not repeat the insane design decision Apple made to have the Pencil charge by sticking out the side of the iPad Pro via the Lightning dock.
We'll have to wait and see how or when this idea is used in a future Surface device and what it might mean for the capabilities of the Pen itself. If the Pen is getting more functionality, its battery life might need a recharging option.