Canon created the LP-E6 battery for the Canon 5DMk2. It's an expensive battery, $100+ in Canada. Canon said that it's expensive because it has its own CPU. Many people have speculated that it's a strategy to "kill" the "generic" batteries. Actually it's not just the CPU but also the significant higher capacity. The benefit of the LP-E6 is the much longer battery life. In the "good old" days, it was very common for a battery to last between 300 to 500 photos.
Canon claims that the LP-E6 last approximately 1,000 photos at 23°C/73°F without the popup flash and 900 photos with a 50% popup flash use.
Here's a poor photo of the battery info on my Canon 7D. It had to be, I was in the field, and I had to use somebody's else point and shoot. My other camera had a long tele without any close focus. But it's good enough to see the battery status: