Just use a torx bit to take out the two screws holding the lock in, then the lock should come out and you can lift the backglass to get in. If you need a key, then take the lock to a locksmith and have them make you one...
Indeed, you were correct. I pulled the screws, pulled the lock, found the bad batteries, found the bad connector, fixed the bad connector (MacGyver job), and put it back in service with a different head lock I had sitting around.