Microsoft Surface Dial Mode D'emploi page 4

Maintain your Surface Dial
To optimize performance of use on-screen, clean the underside of your
Surface Dial with a lint roller or sticky tape. Use a damp cloth if dust build up
requires deeper cleaning.
Your Surface Dial comes with two AAA batteries pre-installed. Replace as
needed.
2xAAA Battery
For additional help setting up your Surface Dial, please go to
support.microsoft.com