Lay device so power button is facing up.
Lift the plastic cover from the center of the device.
Remove yellow rubber dots.
Remove the two 5mm screws with a #0 Phillips screwdriver.
Carefully remove yellow casing.
This might take prying force.
You now separated the black part containing the battery and the yellow case.
Remove the springs and their white casings to easily reach the battery.
Unplug the battery from the motherboard.
Remove the battery by lifting it out.
The battery is stuck with double sided tape and may take some effort to remove.