The Contax is durable but finicky.
You must run CR5's i the handle even if your using AA's and I only use the AA's as a backup to get through the session, then we go to a new CR5.
The contacts between prism, back and lens are also sensitive and must be very, very clean. Take a little alcohol on a swab and lightly clean the contacts, then a lintless cloth and polish each contact like your polishing a jewel. Really polish, not just a quick swipe.
The prism connections are the most sensitive and fragile. Never pick the camera up by the prism or you can break the two clips that hold the prism to the body. If they crack the prism will still mount and feel secure but have an non secure connection to the body and cause the readouts to cut in and out. You can order replacement clips through Tocad (or at least I ordered a few about 3 years ago) and those will fix it, but we never travel with the prism on and once again never pull up on the prism to lift the body.
You can test this by cleaning everything, putting fresh batteries in and place the camera on a flat surface. If you look through it and it the read out goes on and off or is just off press down firmly on the center of the prism and if it connects then you know you've cracked the prism clips.
Now this doesn't mean the contax is fragile and actually mine have gone through more than any camera I've owned. One assistant dropped a body on a blasting white light roof top studio in Miami and it hit so hard the prism bounced off and the ground glass shot out by 30 ft. We put it together and it still worked.
I also go hit by a wave a little north of Miami shooting some lifestyle ads and the wave completely covered me and the camera, even pushing me about 4 feet into a rock reef. I thought the camera and phase back we're ruined and one of the assistants immediatley dried it, but not a drop of water go it and everything worked fine.
(don't try this at home).
Hope this helps.