There really needs to be a note covering removal of BOTH the external battery - and ALSO the internal battery (which means removing the back of the case (simple retained screws) and unplugging the battery inside.

These steps are vital as the battery provides a constant live power rail to the screen even when turned off. Without disabling both batteries there is a risk that, when detaching or attaching the new screen to the cable, a short can happen which can blow a fuse on the motherboard - breaking the backlight.