Follow this guide if the battery is dysfunctional and you want to replace it.
On the back of the device, locate the 3 rubber plugs, and use a plastic spudger to remove them.
Use the T6 Torx Screwdriver to remove all 4 screws.
Using a plastic opening tool, carefully separate the front and back cases.
Using metal tweezers, unplug small white plug.
Slide the flat side of the spudger under the battery and gently dislodge the battery by lifting the spudger up.