Can you remove the cover?
Try using a small flat head screwdriver
Put it in the screw and hit it with a hammer a few times until you can rotate the screw but I wouldn't do that if the broken screw is above the battery
Then you can try the other methods for removing stripped screws but they never worked for me or do this anyway but I'm not sure if it's safe
You might be able to get away with using the next size up phillips head screw driver (PH0). Apply a decent amount of pressure onto the screw as you turn. I've done this on multiple projects in the past. Works most of the time.
One of the screws on the battery cover lost its cross shape. For more problems the battery is swollen.