If you have Microsoft Surface pen for Surface 3 / Pro 3 and it stops work, there are several reasons this might be happening. Here I am going to talk about the batteries. That is right, plural – batteries. This particular pen has three batteries in it – one AAAA battery, and two 319 button cell batteries. If after replacing the AAAA battery your pen is still not turning on, it is possible that the button cell batteries need to be replaced.
To replace the two 319 button cell batteries, you will need to unscrew the pen cap. Just like you would do when you are replacing the AAAA battery. Next you will need to use a Phillips screwdriver and place it threw the battery spring and into the cross-shaped opening in the pen cap. Gently twist and unscrew the inner battery cap. Inside the inner cap you will find the two button cell batteries.
I hope this helps. I was getting really frustrated with my pen until I realized that there were more batteries in the pen cap! Definitely not an issue with later models of the Microsoft Surface Pen.