The differences between the G6 and the G7 are considerable, so I put them into this chart for you:
The Canon PowerShot G7 battery uses a different battery than its predecessor. While the G6 used the BP-511A, the Canon G7 battery uses the smaller NB-2LH , which is also used by the Digital Rebel XT/XTi. That old battery packed a whopping 10.3 Wh of energy, while the one used by the G7 holds almost half that -- 5.3 Wh. And while the G7's battery life isn't half as bad as the G6, it's still worse:
