If you have a Surface Pro, then you know that they stylus is not indestructible like many other styluses (example, HP TC1100). Microsoft has chosen to build a stylus that will eventually break down.
The first issue will be the battery. Yes, it has a battery in it (why, Microsoft?). The battery is AAAA (that’s 4 A’s). A simple twist of the top of the stylus will open the battery compartment.
The second issue will be the stylus tips. I have the same argument here; Microsoft has chosen to create something that wears down pretty easily. The tips are soft rubber. To replace them, buy a tip repair/replacement kit (they are cheap). To replace it, just pull out the stylus from the bottom of the stylus, and insert replacement.
Here are a couple of pics.
The pen broken down with AAAA battery
The tips replacement kit with the battery