The best tools for the job are ifixit's Pro Tech Toolkit. it does include the proper screw driver for this teardown.

There are six screws on either side of the battery that will need to be removed.

These are "triwing" screw heads and require the Y0 screwdriver from the Pro Tech Toolkit does fit perfect.

The screw heads are only 2mm in size. Proper seating of the screw driver, as well as a exertion of some downforce, will be required to make sure the screws can be removed.