Thanks very much for the recommendation! Occasionally I will be unable to use the AF point selector. Removing the batteries and reinserting them usually fixes the problem. Also, on a few occasions I received an "End" error message when I was only at shot 15 or 30. Pushing the shutter button a few times resolved the problem, but the rolls had overlapping frames. (FWIW this problem only occurred 3 times out of 1000+ rolls and only with Cinestill 800.)
Quite honestly I can't say for sure if the problems are battery-related, although certainly cleaning the contacts can't hurt...