A few years ago I opened a Casio WW-31, a very simple and old digital watch from 1984 very much alike F-91W (click for bigger pic)
Now I wonder what the heck should I do to remove the battery cover??? it's a flimsy thing so I probably damaged the watch with unsuccessful attemps.
I'm lucky it's just a keepsake and I don't really need it working.
But I think I will go to the watchmaker for my G-Shocks.... so much for people saying a battery swap is painless and a matter of 5 minutes it can turn out quite frustrating and destructive indeed