espn, where did you get the '10-15 minutes faster' thing from? AFAIK, a clock's accuracy is not affected by small external changes in voltage, esp digital ones, or those that are based on some electronic quartz inside. Anyone with deeper knowledge on clocks care to comment, ie on whether a clock's accuracy is affected by its battery type.
To the original poster: How is this topic related to photography? Just feel a little silly discussing this topic...
;p