Picked up a GL-150 recently with a dead battery. Trying to change it, but can't get to the back. There are two large screws in the back cover (both out in pic 1) and it seems like the whole protective piece will come off. But it won't- I've pulled it as far as I'm comfortable with, and no luck. Anyone know if I definitely have to take off the side screws? Normally I would pop them out and not worry about it, but they're stripping when I attack them with my normal tiny size screwdriver that I use for all other watch screws, so I'd rather not mess with them if I don't have to.