OP: I wouldn't go jumping the gun on this...if the batteries are performing well, then do what the camera says and calibrate the batteries and forget about it. This is a minor adjustment, not the impending battery apocalypse. Those batteries should serve you well for quite some time to come. By the way, if I were you, I'd either get Canon or something extremely well-reviewed...I always had third-party batteries for my cameras and have been very happy with them. Then I got one for my 1D3, and I never once used it...it didn't fit worth crap, thus jeopardizing the entire camera's weather sealing...no thanks. It's still sitting in a drawer somewhere in Canada, even though I sold the camera 1.5 years ago.
Lowner: It's a 1D thing....my 1D3 had to do it while I owned it...I think it's basically that as the battery grows older, the maximum charge it holds is no longer exactly the same as what it held when new...so, even though it may be fully charged to current capacity, it's only at, let's say 90% original capacity...it's never actually "full" as far as factory specs go, and therefore can lead to inaccurate battery level readings (ie: since the current 100% corresponds to the old 90%, it'll read out 90% charge when, in fact, the battery is 100% charged).
So, the calibration drains the battery completely (setting a baseline for 0% charge) and then charges it fully (setting a baseline for 100%). After this, the camera knows what the new norm for "full" is and can start displaying the charge information accordingly (more accurately).
At least that's how I always understood it...but I could be wrong.
