I haven't read through the whole thread so forgive me if I'm asking something that has already been addressed. But is anyone else curious as to the purpose of the CR1616 battery listed in the box contents? That's a nickle-sized, flat disc type battery.
For date/time functions to keep running when you are charging your batteries
It came factory installed on my new 50D and 7D and my CLP 7D. When you read the "Getting Started" section of the manual there is no mention of installing the CRxxxx battery. It's back in the "Replacing the Date/Time Battery" section. I imagine the 40D and 5D2 are the same.
Boy, don't I feel stupid I've been shooting with a 5DMKII that I bought new a year ago and I swear I don't remember seeing or installing this battery. But I just looked in the manual and sure enough, there it is on page 217. Did this come factory installed on the Mark II?