Wedge your fingers between the upper case and the lower case, starting from the rear of the MacBook between the hinges.
Lift the lower case only slightly to avoid damaging the cables that connect the lower case to the upper case.
Keeping a firm grip, lift steadily until the lower case separates slightly from the upper case.
You may experience a lot of resistance when lifting the lower case. If necessary, slide an opening pick or other ESD-safe pry tool down the side edges of the lower case to pop the two hidden retaining clips free.
During reassembly, to re-engage the clips, press firmly near both side edges of the lower case (near where the pick is inserted in the third image) until you hear the clips snap into place.
Use the flat end of a spudger to press and hold the small gold 'battery disconnect' button.
If the power LED is lit up, continue holding the button until the LED goes dark, and then release. This may take up to 10 seconds.
If the LED does not light, release the button after 5-10 seconds. Press and hold it again for 5-10 seconds, and release. Finally, press and hold it a third time for 5-10 seconds, and release.
This step ensures the MacBook is fully powered down and safe to work on.
Remove the single 2.9 mm T5 Torx screw securing the battery connector to the logic board.
2015 models have a silver grounding clip with two foam pads directly under this screw, which may come loose. Be sure to reinstall it during reassembly.
As an added precaution, you may physically disconnect the battery by inserting a battery isolation pick between the logic board and the battery connector.
Use the flat end of a spudger to disconnect the USB-C port cable bracket by prying it straight up from the logic board.
To reconnect this cable, first line up the metal bracket over the screw holes, then press down on the middle of the bracket. Make sure it's aligned correctly, or you may damage the connector.