This is what happened on my Leicaflex. The original mercury battery had leaked and corroded inside the battery compartment, locking the retainer to the body. I finally had to chisel a slot into the battery retainer and use a big screwdriver on it.
Once inside, the compartment was in surprisingly good shape. Even the bakelite (or plastic) parts looked good after a clean up. But the second I touched the battery prong, it broke off and dropped into the body somewhere. The battery juice had eaten it in half at the bend.
It's probably still in there. I'm handy w/ tools, but know better than to open up a Leicaflex, a camera so complicated that it almost led Leica into bankruptcy. I ended up selling it as a meterless camera, and it worked just as well that way. It also still weighed as much, so it's not missed.