Check that the original battery cap/door of the camera has been removed (please reference the diagram in the manual in section 3).
Use the screwdriver that was included in the pack. If it is too small, you can use the screwdriver that was initially sent when you purchased the Deep Sentinel system.
If you've misplaced both screwdrivers, you can use any screwdriver with a small/medium cross-head.
Check that the grey lid of the USB Battery is rotated counterclockwise (like you are opening a jar). Align the dot on the grip side of the USB Battery with the dot on the Camera and insert. Turn the grey cap of the USB Battery clockwise to tighten it onto the Camera.
If you're still having issues, check out this video: