How to Take the Back Cover Off a Nook HD
The Nook HD was never intended to be a user-serviceable device, and it's not an easy device to disassemble; removing the back cover almost necessitates a complete removal of the case. Trying to get at the components inside the Nook may damage the case, and will void the warranty. However, there may be times when you need to access the battery or to adjust the positioning of the Wi-Fi antenna. It can be done with the right tools and a bit of effort.
Hold down the power button until the Nook is completely powered down, then place it face up on your workbench.
Insert a flat prying tool between the surface of the screen and the inner edge of the bezel around the sides of the device. Slide the tool around until you get the tape inside the bezel to come loose. Slide the tool around the inner edge of the bezel until the tape is loose on all sides of the device.
Slide your prying tool under the bezel at the corner closest to the carabiner hole. This is the thinnest part of the bezel; once the tool is pushed in, the edge will rise up. Put in a second prying tool to prop this corner of the bezel up, and work the first tool all the way around the bezel, working to loosen the tape further and trying to pop the plastic posts out of their grommets. Those plastic posts are fragile, so be careful with this, and use the least force possible to pop them open.
Remove the front bezel from the Nook HD.
Use your T5 Torx screwdriver to remove the screws around the outermost edge of the internal metal bay. Only remove the outer screws. The ones closer to the screen hold other parts of the Nook's internal components in place, and do not attach to the back of the device.
Lift the metal base out of the back cover. Be careful of the battery cable, which attaches to the back plate of the device, and the Wi-Fi antenna, which may be loose against the electronics in the back of the Nook. Once you can get to where the battery cable connects to the main board of the device, detach it carefully, then finish removing the back cover of the Nook.