The Canon BG-E6 Battery Grip is designed specifically for the Canon EOS 5D Mark II
Comes with Genuine Canon Australia Warranty
The Canon BG-E6 Battery Grip holds two Canon LP-E6 Batteries that deliver double the number of shots or video time from the 5D II. Alternatively, use 6 AA batteries in the included Canon BGM-E6 Battery Magazine.
Since the AA batteries are not chipped, the 5D II is not going to show you detailed battery information when using the BGM-E6. Though the BGM-E6 is a nice feature, I don't personally find it useful. Even if you only have one LP-E6 battery, the BG-E6 still functions fine.
Back to the grip. The Canon BG-E6 Battery Grip is very solidly built - it matches the 5D Mark II well. They share a magnesium alloy frame and the BG-E6 retains the sealed battery compartment. Most of the controls present on the built-in 5D II grip are also found on the BG-E6 including Shutter-Release, Main Dial, AF Point Selection, AF/FE Lock and AF-ON. And, don't forget the power on/off button