Troutbum, thanks for your suggestion.
As I've mentioned before, I really suck at working with tools. Anything I try to work on, it seems I either put it back together wrong or something breaks, to the point that I've accepted that I must be cursed.
Since I have no other choice and the job of undoing a total of 4 screws and pulling the battery out seems so simple, I figured I would be try it while making sure I was SUPER careful not to force anything.
I was so happy that maybe this one time I was successful in not breaking anything but Alas! My misfortune continues. When I pulled the battery out, I noticed a piece broke off right where that red mark is. How could that happen? I didn't even touch that piece, let alone force it.
Anyway, I got the battery out and will be ordering a new one today.