The screw at the battery compartment

You could try different screwdrivers. Generally only the center of the screw strips. Using a screw driver with a larger tip may work. If you have already removed one if the screws, wrap some tape around the threads (so it is harder to lose if you drop it) and take it to the hardware store or a good Electronics store (one that sells electronic parts Radio Shack or better). Put the screwdriver in the screw head and try to wiggle the screwdriver back and forth, it should not wiggle at all (there should be no 'play' in the fit). Look at the fit from the side. You want the screwdriver tip to 'fill' the slot in the head of the screw, a little more is ok, less concentrates your effort on less metal and bad things happen.

You can also try a small (good quality) straight blade screw driver. Sometimes there is enough metal left for them to grip. Note: Now is the time to buy that good quality screwdriver you have always wanted. Cheap will most likely make things worse.

It is impossible to do it and I tried with a really small screw driver