I am not entirely sure if this model is rechargeable. The available information suggests that the Surface Pen with product number EYU-00010 has a rechargeable battery and is charged via compatible Surface accessories or devices; if you actually mean the Surface Slim Pen, it is charged wirelessly in a charging cradle, the Surface Pro Signature Keyboard, or the Surface Laptop Studio storage tray. There are no clear charging instructions in the data for this model. If you are not sure about the exact type of pen, it is quite possible that your pen uses an AAAA battery instead of a rechargeable one and is therefore not rechargeable.