When Apple revealed their new Apple Pencil this past September, the reaction to how the iPad Pro accessory would be charged was mixed. Some thought it was ingenious while others thought it was an awkward and inconvenient method. While Apple has a patent pending idea that docks their pencil directly into a future iPad, it's unknown whether that design will ever come to life. While today's Surface pen from Microsoft works with batteries, that's likely to change if one of their latest patents comes to life. The U.S. Patent & Trademark Office published a patent application from Microsoft earlier this month that reveals they're working on a new rechargeable Surface Pen and docking system. Microsoft notes in their new filing that "a stylus may provide active functionality that is powered by a rechargeable battery. A charging circuit within the stylus may provide charging current for recharging the battery via one or more terminals configured to contact charging contacts of an associated stylus charger."
Interestingly the accompanying patent figures always show their new pen-dock as having an open or cut-off end and is never displayed as a standalone design. This could strongly suggest that Microsoft is strongly considering building it right into their Surface Pro or Surface Book hardware.
Interestingly the new Surface Book design includes an odd dynamic fulcrum hinge as noted below that doesn't allow the Surface Book to fully close flat. This oddly could end up being the ideal position for the newly proposed Surface pen-dock and part of the original thinking for why they chose this new hardware design twist to begin with. For more on this new invention, see Patently Apple's full report.