This confirms what I suspectedthe new MacBook Pro battery has a lower capacity than the old one. About 16 percent less to be specific. The old battery was rated at 5600mAh/60Wh, but the new ones are rated at 4700mAh/50Wh. This perfectly explains why you now need to use the integrated Nvidia GeForce 9400M on the new Pro to get the same five-hour (rated, not real world) battery life as you did with the discrete 8600M GT on the previous-gen Pro, despite its use of more energy-efficient DDR3 memory (which would negate drops from the faster FSB) and the same processor clock speeds.
-Gizmodo
-Gizmodo