Whilst hiking at Shelby farms today carrying my mamiya 645af, something annoying and strange happened. When I was leaving the car, I loaded a roll of film into the back, it advanced fine, no sign of lag or anything. Halfway through the hike, I switched the camera on and noticed that the indicator on the back showed two dashes instead of a number. I pressed the shutter, the camera fired, then the back began to advance like I had just loaded a new roll. This kept happening until the back reached the end of the spool and actually was trying to expose leader paper. I changed the roll, thinking it had lost track of the markers on the backer paper, the back did the exact same thing again. I noticed that the back would cycle back to loading whenever I would turn the body off. It became increasingly apparent that the watch battery in the back was dying. An expedited mile hike back to the car and a hurried drive to the walgreens ensued, with the camera body on to power the back all the while. I replaced the little cr2032 battery and everything went back to normal. I now have a spare in the bag, but I am wondering if there are any warning signs which would have alerted me to this problem?