Tasco OS36 Binoculars battery replacement

Question

The red light in the compass of my Tasco OS36 does not turn on when I push the button on the top of the housing. I am assuming that it needs a new battery but when I unscrew what appears to be the battery compartment on the housing there is a s***w shaft on the underside of the "cap" which penetrates the center of a white plastic disc and fastens into the housing underneath this disc. The disc does not appear to be easily removed. I cannot identify any other fitting which would be the battery compartment. How do I get the light to turn on?