Breathe deeply. Trying times are ahead, but we promise the lower case does come off.
Push the thin rims of the lower case surrounding the battery compartment in, bending them past the tabs, and then lift up to free that corner of the lower case.
By using a T8 Torx screwdriver to remove and reinstall the three hex screws on the bottom case as suggested, I ended up stripping the screw heads when tightening them. By pushing hard on a T9 Torx driver I was able to carefully remove the stripped screws. I would recommend using the proper size hex driver instead of the T8 Torx driver for a more positive grip in the screw head.
To add to my above comment: There doesn't seem to be a correct hex size for these 3 screws in either metric or SAE. Actually, the T9 Torx driver works pretty well. I replaced the stripped screws with three brand new ones.