The ist D has a backup battery, a button CR2016, that is used for backup. If you look at the bottom of the camera, there's a screw-in round cover. That's the backup battery.
The manual says "change it once every five years". Not that I read the manuals either, but hey. j -- Juan Buhler http://www.jbuhler.com blog at http://www.jbuhler.com/blog
