Are you able to change the battery?

It is possible to change the battery in this model of iPod nano, although it requires taking the battery off the back of the display assembly (which it is adhered to) and de-soldering/soldering it to and from the logic board. As there is no ifixit guide for this at the moment, here is a video on YouTube which demonstrates how this is done:
https://youtu.be/U_N55_Tdz2U (Perform at your own risk!)

There likely hasn't been a guide created for this as it is out of the question for the average ifixit user due to the requirement of soldering (Although I do know of similar guides that do exist on ifixit so it may just be that nobody has created a guide yet)